I am not personally hoarding them but I can see the purpose to more than one. I don't need or want 30...but 3 seems like a good number. Build one as a pistol and two as rifles. It means I have a "spare" rifle I can loan a friend if we are going to the range together and not sharing a bench, or going varmit/coyote hunting or whatever. It also means I can keep one lower for, say, all my .223/5.56 uppers and one dedicated to my "bigger calibers" like building one as a .300 blackout or .277 Wolverine and leaving that upper on it. Or keeping one as an HD gun with a 16" upper and having the other one keep whatever other upper(s) on there.
Or heck one as a rifle, one as a pistol and one that might never get built. On the last if for some crazy reason one/both ARs get stolen in a break in or something I've got a lower I can build out again. Same thing if laws change some day and something happens to one of my built ARs. You can't replace a lost/stolen "banned" gun in Maryland. You can have a defective one replaced by the manufacturer...but that is it (I assume that would cover replacement for a damaged one).
Some like the Anderson lowers are cheap enough buying that one or two spare isn't a big deal. Even just getting in to ARs that is just my 2 cents on it. I won't call those with 20 lowers and a dozen built rifles crazy...but it does seem a little extreme to me :-)
