Why for a number of reasons:
1: The main reason is you need no other program, ie third party program such as uoam (to load in your sos's) or uoassist (to set macros) plus whatever other things needed such as uorudder (steering) or using mulitple keybindings in the 2d macro system to left right etc etc. KR is all in one. Other than excel which is basically a mass data entry utility in this case you need nothing else.
2: The second reason is by manipulating the xml you can enter in hundreds of sos's in one go, rather than how you had to do it in uoam by entering each as a separate data creation entry by placing a label. Even tho you still need to manually enter the coords into both, creating labels is way more time consuming than using data entry in a straight spreadsheet format which is 1000% times quicker with tab and enter and to copy and paste the text into the waypoint xml takes all of 5 seconds.
3. Looting the chests in KR is magic, because all the chest loot is presorted into Gold, items, scrolls, regs, gems, nets from the top down in the chest so basically you can grab what you want without wading through tiny jumbled 2d backpacks for it. When you have 45 items in a chest and you really only want the gold, and gems or gold and scrolls etc you will instantly see the difference in time and effort to loot chests. This ALONE would be one reason to fish in KR not needing to mess with loot and seeing at a glance what you want out of chest without needing to wade through the lot.
4. The KR zoom functions and waypoint settings show me ON SCREEN where my sos is, by adding an ingame icon to show in game and and icon on the map so when fishing i can zoom out on the map, see where it is and head in that direction etc. As I get closer I just zoom in.
5. The KR macro function allows you to fish in one spot at the touch of a button or keybinding. Depending on how you set it up you can fish for a long , long time before needing to rehit the macro, tho generally the fish will stop biting before you stop fishing lol, and to fish continuously while sailing, while you still need to 'target' the water, you can sail half way round the globe never needing to touch your macro, just click the water (This would be fixed as soon as someone in the dev team allows a fishing pole to be added to the target by resource function *hint*, or a 'target relative' *hint' function is added) but still, I have never had any problems just clicking the water as long as I don't need to have to click the pole lol and target.
This first pic shows how my desktop is setup for fishing, you see the blue glowing dot in the ocean that is the spot of an sos. Obviously the pic is greatly reduced in size as my monitor is 22" widescreen, however you can also see my boat controls, my backpack open, my bugs pack open and the jnl and map.
This pic shows a zoomed in pic of the map, my boat is the little black dot near the lower sos position.
Because I can enter a whole bunch of sos's really easily once entered you can zoom your map right out to a 'world' view to see where clusters of sos's are to determine which area you will fish.
The area we were just looking at is circled in the above pic, so as you can see it is so easy at a glance to see where I need to go next once I have fished up all the ones round skara. While uoam lets you see you are constantly needing to change the view settings etc to get the same thing and doing it in KR is so much easier as is just a mouse wheel zoom in and out which you can do while you sail and fish along. Getting a world view in uoam is a pain in the butt unless you run it on a dual monitor. Plus it is not on your screen and you are flicking between tabs to get the same functionality.
KR, also gives you the option to just fish using the ingame icon and not use the map at all but just cruise around til you find a blue dot. This can be fun sometimes if your just out to get serps but don't want to sail past a chest spot on your way.
Like I said I have fished for years in 3d then 2d and now KR and for my money you can't beat KR for functionality. Now if the devs implemented a multi data entry point for sos's that actually put the sos where the darn thing is we would be 10,000 times better off lol, and could do away with excel, however, the excel sheet takes all the pain out of data entry so until such time as something better is implemented then for me it is the only way to go.
"OH" !!! and another great function of being able to add in sos's via xml is if you regularly fish with someone you can send them your waypoints to add to their map, just make sure you use a different icon set to the ones you use, and it means whoever has the boat key can steer in the direction of the nearest sos, irrespective of whose it is. At one point I had my map set with the sos's of 2 other players when we fished regularly together, just meant manipulating the xml which took five minutes before an outing with their new code and updated sos's if they had added any, by deleting what you put in them before and refreshing with the update.
Regards
If you play KR and fish, this is great for you 
, if you don't well it does not bother me in the slightest 
*wanders off mumbling something about uoam, uoassist, uorudder, uo illegal programs, me heartys!!*pulls out sextant wonders which museum to put it in 
*
