2L, 3L, & 4L all have a built-in liquid rate set by the open market for ANY .com, via expiring domain, no-reserve auctions, BIN listings, and any auctions that result in a successful public sale.
However! 5L do NOT have a set price for ANY .com, so the 'guarantee' is removed and risk is great. It's true that SOME 5L's are selling, but not ANY 5L... just a select handful.
This all could change overnight, random 4L didn't have much value, now they are highly sought after. Maybe 5L's will be next! But for now they are just speculation without quick liquidation