If you apply to jobs where the stack advertised looks like it's from a decade or more ago, you might have to actually deal with technology from two to three decades ago (or not, but it's probably more likely). People like new things, and often switch jobs looking for something new, and in tech that's often new technology they've played with but not got a chance to use in production.
Honestly, something that's advertised as ruby/python and HTML will probably put a lot of devs off that used to happily do that all day, and so a company might have to pay higher for good talent, or put up with worse talent applying for the same salary.
You might actually be worth more not knowing react. Communicating that to prospective employers might be hard though.
In other words, you can probably make really good money slinging COBOL if you know it and can communicate your talent sufficiently for the same reason, but more extreme.