You have to confirm your resignation. At least on the web interface; I haven't played on mobile for a while but I'm sure it's the same there.Â
So, it's not like the player accidentally resigned. Removing the option, Â even in cases like that, Â would either force the player to continue playing or just abandon the game instead of just resigning like they can do now. It doesn't really matter if resignation at such a point makes sense or not.

I believe my opponent in this game mistakenly hit the resign button when he meant to hit the draw button here which would have offered a draw in this scenario after black's 50th move. However, when he hit the resign button, he lost the game in a perfectly drawn position. There was no way for white to lose the game (even on time as black had just the bare king). So to make matters more fair, I think a good idea is to remove the ability to resign when the opponent has just his bare king.