Why no Gate APC?

I got to thinking after rewatching a few SG1 episodes where they “can’t go through the gate to help SG1, it’s too heavily fortified by Jaffa”.

Why do we think they never created like an armored vehicle that would fit through the gate they could send in with other SG teams inside to safely create a foothold in enemy territory? Other than the obvious “well then that would make things easy and we need a plot for this episode”, what would have stopped the SGC from using those types of vehicles?