Based on what I watched as a kid during the ATC era, Ernie didn't have speaking roles very often, if at all. That was left to other newer Muppets like Elmo, Zoe, Rosita, Benny Rabbit, Ingrid and Humphrey, Baby Natasha, etc. Puppeteer availability also has something to do with it: Steve probably wasn't as available as other performers like Caroll Spinney, Jerry Nelson, Kevin Clash, Fran Brill, Marty Robinson, and David Rudman. (On a side note, Muppet Treasure Island was being filmed in the mid- to late 1990s, so that might be another reason why Steve wasn't around to play Ernie.) But by 2000, Ernie had major roles in street scenes like in Episode 3909.