One thing is pushing a battle droid a bit so they fall and another is stopping a bullet traving at near sonic speed dead in its track, even redirecting then would take considerable effort.
Also there is the factor of time, a bullet would take a second to reach its target and the movies shown the Jedi always have to concentrate for a few seconds.
Also please do notice they always raise their hand before trying to do that, one thing that shows Anakin/Vader power is that he was able to rip parts of machinary and move then around without even needing to make such focus.
Oh and in droidekas case ...
Well to start there were no major conflicts for centuries, there was no need to outfit what is pretty much the local militia with such dedicated equipment as it would be a waste of resources, besides there is still the fact its a melee weapon and you have to run to a droid outfited with 4 blasters (or if you prefere, 2 double barrel blasters), its best to keep behind cover and wear the shield down or use granades.
Also notice that even Qui Gon did not wanted to go up to then and slice then, my guess is they would simply roll away and resume fire.