These started being removed in 1998 (with Ghostbusters being the exception), with Terminator and ET lasting until late 2003. The majority of them were on 528 westbound. Their fiberglass shells only lasted about 3-4 years in the sun, so they would be continually replaced. All of them also had lighting effects.
The biggest factor in their removal was that Universal needed to advertise the parks as a resort instead of a single park, and with billboards along the tourist corridor being prime real estate with 10+ year contracts, it made sense to take them down and start advertisements for the whole.
There were billboards for the following:
ET - light up finger
BTTF - light up flames behind the time machine
Jaws - light up headlight on the boat facing the shark
Kongfrontation - light up tram
Terminator - light up eyes on the T-800
Ghostbusters - illuminated proton streams
Earthquake - illuminated fires
If you guys like factoids, the Jaws billboard was also repurposed for the display at the Universal store in OIA.