Why not? Why would you want to get panzerjaegers if you can just have mines\AT gun\marder?
If you're talking about the AT rifle infantry, then it's probably because they can be upgraded with an LMG plus they can repair tanks plus they've got the gas shot ability. But realistically if they aren't going to be able to do any damage to allied mediums up, it's pretty much like having a squad missing a model you can never reinforce back to full health. Imo they're also going to be a dead weight.
It's like the M-42 in coh2 lol. You can fight off some lights, but then after the mediums come out the best it can do is support infantry in killing other infantry. And it can't even do that well.
The difference being that we're talking an actual mainline infantry squad that has to give up on two actually good upgrades just to fight off an LV in the early game.
It's like a jack of all trades but not actually because it can only perform one role in an okay fashion until it can't, and then it's stuck performing the other role it's mediocre at for the rest of the game.