I don't think the problem is in the developers but rather the employers, especially the recruiters. They love to find a developer that is a perfect fit in terms

I don't think the problem is in the developers but rather the employers, especially the recruiters. They love to find a developer that is a perfect fit in terms of stack. If A developer is a better coder than B but if B has experience in the companies stack, they will put B as a higher priority. This makes sense since people can't tell which one is a better programmer by looking at resumes. So what does a startup developers do? We have to chase after those shiny and new stack to keep up with the trend and be high in the market. When we are looking for an another job, which job do we apply to? The one that is closer to your stack. You will be high in the market and get to say "I have experience". Because these are the things that recruiter/employer cares the most.