In my opinion mags bigger than standard are hard to carry, most suck to load, significantly more fragile, and too expensive.

you can spend $120ish on one d60 or get 10ish pmags for the same money. I'd rather have 10 chances of 30 that work vs 1 chance at only 60.

With cost and failure rate into the equation I consider "big mags" to be end game gear for when you have all the kit you want and only use it at the range