When I look up early photos of SWAT teams, none of them appear to be wearing helmets, though. paralleling to the films. But if I look at SWAT Teams on google images of today or from the 2000's, all of them appear to wear helmets.

Circa 70's:

https://static01.nyt.com/images/2014/09/06/multimedia/retro-swat/retro-swat-videoSixteenByNine1050.jpg

http://www.impdphotography.com/keyword/team/i-s7h4swf/A

Circa late 80's/early 90's:

http://static1.squarespace.com/static/52fe40dde4b053964a5a8749/52fe4772e4b0eb1e35952205/54243c3de4b0dca82631f284/1412858666380/?format=1000w

https://www.co.merced.ca.us/images/pages/N424/SWAT_TEAM_PHOTO_1986.jpg

https://www.google.com/search?biw=1920&bih=950&tbm=isch&sa=1&q=swat+1991&oq=swat+1991&gs_l=psy-ab.3...3543.4998.0.5054.9.9.0.0.0.0.93.533.9.9.0....0...1.1.64.psy-ab..0.7.428...0j0i67k1.sO0FP_Llv8o#imgrc=4MvSHclXeoWABM:

Why didn't they wear combat helmets back in the day? Was it resource issues? Monetary problems concerning police budget?