If you're serious about making music with keyboards, there are a lot of reasons why you would be spending anywhere from $800 to $3,000 on gear just for your basic setup. At these price points, you have the option to get analogue gear, and the tradeoff is that the analogue gear is less flexible (it's not more expensive).
I'm not trying to pick on people for using inferior gear, but explain that the people who spend more money on a keyboard are making very rational decisions. Just to pick your Pianoteq example, once you pair a $150 Pianoteq license with a $500 decent quality weighted MIDI keyboard, you're already in a price range where you could get good analogue gear if that's what you want.
Once you're spending $1k, $2k, $3k on gear, your main questions are going to be about things like ergonomics, personal taste, capabilities, etc. Not everyone is okay with using a laptop, getting a good laptop for use on stage has its own problems, and laptops add to the price. This isn't really that different from the amount of money you'd spend to get into other instruments, and is actually kind of cheap when you compare it to something like a concert violin--you'll even see high-school students with $5k violins, and I'm not talking about kids with rich parents, either.
Again, I'm not saying that there's something wrong with going for a $100 keyboard and your $180 license for u-he Diva. That's an excellent combo. Just trying to explain that there are reasons someone would want to spend much more money in the first place (ergonomics, portability, keyboard feel, etc.) and at those price points, analogue is an option.