To offer some additional causes for the degradation of UX:

1. An increasing part of industry profits started coming from entertainment (or worse, psychological exploitation) instead of selling the customer a useful tool. For example, good budgeting-software has to help the user understand and model and achieve a goal, while a "good" slot-machine may benefit from confusion and distraction and a giant pull-handle.

2. "Must work on a touchscreen that fits in a pocket" support drags certain things to a lowest common denominator.

3. UX as a switching-cost for customers has started happening more on a per-product rather than a per-OS basis. Instead of learning the Windows or Mac "way" of screens and shortcuts, individual programs--especially those dang Electron apps--make their own reinventions of the wheel.