Well, not that I endorse the position but...Wait, first, a spell book looted from the big bad has the same zero cost and is MUCH more of a common thing than just finding a scroll of force cage. Second, I've played several fighters in this game and every time I had to buy the plate armor rather than find it.
It's not a ridiculous claim, and you just declaring it so without any support isn't persuasive. Your complaint about wizards scribing is literally the first I've seen of it's kind in the over 5 years 5e has been out - here, or at Reddit, or the WOTC boards before they shut down, or anywhere else. You thinking you're speaking the obvious smacks of you living in a bubble and having not considered for a moment the possibility you might be off on this topic. Take a moment and consider - is your experience maybe differing from others by a large degree? Or do you even have the experience with this topic in 5e at the table at all to be declaring other people's views ridiculous for dissenting from yours?
A found spellbook is useless until you scribe its dpells into yours. 5e foes not allow free use of captured spell books. Yah still gotta scribe.