Last job, we started writing mixing bits of Kotlin in an otherwise mostly-Java in a monolithic Spring-based service. Good experience.

One reason (among many) is that employment in American companies is less stable than in Europe with strong employment laws. Twitter could not do the same type of layoffs in Europe, with stories like this one being pretty common. But this safety net has a cost, and the cost is a part of total employment cost for employers. Whether the safety net is worth it for employees in IT, that's another matter—but it can't not be taken into account because of the law.

BTW, in some European countries there is a strong culture of IT workers doing long-term contractor work exactly to trade off employment laws for (usually quite a lot) higher wage.

I found it crazy useful to study old, established, mature technologies, like relational databases, storage, low-level networking stack, optimizing compilers, etc. Much more valuable than learning the fad of the year. For example, consider studying internals of Postgresql if you're using it.

I'm not a person who'd be loyal to a brand. Yet Motorola consistently produces devices that turn out to be the best trade-offs (price to functionality) for me. And, so far, all these devices were pretty durable as well, though it's not that I really put smartphones into lots of use. That's all I can say.