Tbh humans are creatures of procrastination, always leaving stuff for "later", content having a deadline will probably push some to finally do it instead of postponing it endlessly and ending up never doing it at all.
Both the preorder allied races and "limited time content" like mage tower and field medic are serving to fill a bit the infamous "end of expac content drought", it's shorter than usual but still most people ran out of content by now, so the list of stuff "do this before BFA" helps to patch it.
I have an impression if someone hasn't done it by now and thinks they'd do it somewhere down the line 2 years later, they're deluding themselves, they'd probably never bother at all.
Yep, it bothers me from time to time I've never levelled a monk in MOP so I haven't gotten the MOP challenge set for monk, but in everyday's play I'm really not impacted by it. Saying I'm losing sleep over it would be overblowing it out of proportion.
Anyway if anyone still needs mage tower done - just do it (tm). There's plethora of guides both how to quickly & efficiently gear an alt for it, and what's the strat for the challenge. Stop postponing and get to it.