The reason is more practical. The only effective use of tear gas is against peaceful untrained civilians. It doesn't work against looters and vandals because they are highly mobile and aren't going to stick around long enough for tear gas to be effective. Provocateurs and ex-military are trained against the mind game that tear gas is. I know this because I've stood in a tent filled with tear gas reciting the UCMJ while my unmasked sergeant looked on, himself seemingly unaffected by the gas. Tear gas does not affect an individual trained in it. The only people you're instilling fear into is untrained moms and dads and children who are peacefully exercising their 1A right to stand there and breathe it in.

The use of tear gas is unconscionable mainly because it's a waste of taxpayer dollars. Its only purpose is to make its user feel strong laying waste to crowds of unruly women and children and stop them screaming at you.