They are. EW and IR C-UAS has been productionized over the past decade in most countries, but there are still supply chain and cost blockers around power electronics and they tend to be treated as a last resort because of their indiscriminate nature.
Only if one understands the different failure modes, but either way the average HN reader shouldn't try this at home or you'll get in trouble with radio spectrum pollution.
Probably because currently they cause more collateral damage than is useful. Your own equipment will be damaged too leaving a bunch of unguided soldiers with just their guns and rations that are still an obstacle an enemy can't walk through, and it will piss off anybody within 1000 miles when you start disrupting their telecommunications with random noise if not cause actual damage. If they are powerful enough you could potentially cause some mistaken nuclear blast warnings too, although perhaps without a gamma ray component it would still be rightfully ignored.