A couple of things. First you didn’t seem to put that much flavor into the slow cooker. Salsa has a lot more stuff in it than canned tomatoes which is why you see so many people say “just dump in salsa and chicken and bam you have tacos”. Also diced tomatoes might not be the best … consistency? Like a jar of tomato sauce with a little extra liquid would have probably come out better.

Finally (this will be unpopular) throw out your slow cooker and do the same thing in a dutch oven. I realized this by mistake when I was making food for a big party and made two batches of the same thing by those two methods and then I swapped all of my slow cooker recipes to dutch oven on low heat in the oven and then I gave my slow cooker away.