If you work in a good area (which you want to for tips, anyway) your chances of robbery are pretty low. I've delivered pizza since 1998 and never been robbed. I've personally known of a handful since then, but literally 5 that I can think of. 2 were in the area of the crappy apartments S of the astrodome, and the store (Pizza Hut on Holcombe and Main) stopped delivering there at that point.
I think if I did Uber, even part time, for 20 years, a robbery would be inevitable. At least with pizza delivery you control where you work by only working in certain stores. That's not true of any of the apps, whether food or people.
Because labor is controlled, if it's slow there are less drivers scheduled. So if you're a good driver and employee it may be slow, but if you're one of only a few drivers you'll do ok even if the store is slow. If it's busy it can actually be a detriment as the managers will tend to overschedule and you can actually make LESS money. If it's crazy busy then you're ok, but quite often I do better when it's fairly slow because there aren't as many drivers scheduled.
Unlike uber, labor costs exist...