Then you're not doing the math. Let's look at just 5 of scrolls at random, using Odetta at the central Luna mage shop on Atlantic.
Fire Field sells for 27 gp.
Greater Heal sells for 26 gp.
Lightning sells for 1 gp.
Mana Drain sells for 29 gp.
Recall sells for 18 gp.
Costs:
Fire Field = 1 Black Pearl + 1 Spider Silk + 1 Sulfurous Ash
Greater Heal = 1 Garlic + 1 Ginseng + 1 Mandrake Root + 1 Spider Silk
Mana Drain = 1 Black Pearl + 1 Mandrake Root + 1 Spider Silk
Recall = 1 Black Pearl + 1 Blood Moss + 1 Mandrake Root
Let's assume you don't have tens of thousands of regs sitting around (found/bought at a cost well below NPC prices, normally), and you need to actually buy all supplies.
Scribes Pen: 8 gp. Let's go low and assume only 50 uses per pen, so 0.16 gp per scroll.
Black Pearl = 5 gp
Blood Moss = 5 gp
Garlic = 3 gp
Ginseng = 3 gp
Mandrake Root = 3 gp
Spider Silk = 3 gp
Sulfurous Ash = 3 gp
blank scroll = 5 gp
Fire Field = 1 Black Pearl + 1 Spider Silk + 1 Sulfurous Ash = 16.16 gp per scroll
Greater Heal = 1 Garlic + 1 Ginseng + 1 Mandrake Root + 1 Spider Silk = 17.16 gp per scroll
Mana Drain = 1 Black Pearl + 1 Mandrake Root + 1 Spider Silk = 16.16 gp per scroll
Recall = 1 Black Pearl + 1 Blood Moss + 1 Mandrake Root = 18.16 gp per scroll
So now let's assume you did as suggested, and 100% LRC means no reg use. You also have zero waits, other than the time each scroll takes to craft, because you got rid of the mana requirement. So now I can make 50 of any of those scrolls in a minute or less. Notice how Lightning on that NPC is already selling for 1 gp; someone's already driven that buy price down the minimum 1 gp. Now your cost to make any of those scrolls is instead 0.16 gp.
Fire Field: over 26 gp profit per scroll. 1092 gp profit per pen
Greater Heal: over 25 gp profit per scroll. 1042 gp profit per pen
Mana Drain: over 28 gp profit per scroll. 1192 gp profit per pen
Recall: over 17 gp profit per scroll. 642 gp profit per pen
That's better profit than selling ingots to smiths.
Now think about just how many scrolls there are. Now think about just how many NPCs there are on every single shard who buy scrolls. 1092 gp doesn't sound like a lot. That's 65.5k per hour. 1.57m per day. Still doesn't sound like a lot, but we're talking but we're talking something that can be done on a hidden char, is 100% safe, and where the "hotspot" GMs would have to watch for scripters is... every single mage/scribe/etc shop on every facet on every shard. Ie, it essentially can't be policed. So you just park trial accounts and have the chars make free gold.
Folks here often talk about how they've never been rich in UO; I see people saying something like "I maybe have 30m in the bank, and that's more than I've ever had before" all the time. That 1342 gp profit from a pen... That's 574m profit per year, per char the scripter bothers to do it on... that's at least 10x the profits carto ever allowed, and look how heavily that got scripted.