Back then, hip hop moved at an accelerated pace. You see how Drake, Kendrick, and Cole are still successful after 15 years? That would be impossible to do in hip hop back then. You were lucky if you were still relevant by your fourth album.
Kane was a fantastic MC, but he stopped caring about the music he was making at some point. He said that he started doing whatever he wanted because of the way his deal was structured with Warner Bros., so he was just cranking out as much music as he could. He had a crush on Barbara Weathers, so he did a song with her. He was a fan of Dolemite and Barry White, so he did songs with them. He leaned so much into the R&B/player side, he lost favor with people who wanted the raw battle MC.
He tried to go back to that on Looks Like a Job For... and he initially blamed the producers when it didn't sell. But then he realized that by '92/'93, hip hop had changed so much to the point where guys were rapping behind the beat, and he was still rapping like it was '88 with the speed flow. Uptempo records were his bread and butter, but those songs were considered ancient by the time Illmatic and Ready to Die came out.
Kane had the ability to adjust with the times, he just didn't. Rappers had way shorter careers back then. It happened to everyone. The irony is when Kane came out in '88 and set the world on fire, guys like him were replacing Run-D.M.C. who were the kings at the time. They went triple platinum with Raising Hell and became crossover stars. Tougher Than Leather took two years to come out and it sold half of what Raising Hell sold because by '88, Run-D.M.C. was starting to get looked at as old-school next to Public Enemy, Rakim, and Kane. And if you listen to that album, they're fully aware of the culture shift and adjusting their sound to fit in.
If Kane's first album was twenty years later, he would have lasted a decade and a half also. He would have the talent and the ability to move with the times. Or he would at least be relevant for more than two albums. His problem was that he strayed too far from what made him popular and tried to gain an audience that were only going to stick with him for a short time, then move on to something else.