Just as an example, in Vancouver, I got poached by a recruiter from G&E to work with FPGA in a senior position. The offer was around 80K.
At London a senior embedded systems engineer would get 40-45k pounds.
A senior fullstack / devops / backend dev at any of those cities can clear around 50% more easily with 10 times more jobs available to pick from.
Embedded systems don't really scale the same way backend systems do. In embedded, you write the firmware, and it gets loaded into thousands or millions of devices. There may be a few updates, but firmware kind of gets frozen in time.
With backend, you write code that can be used to expand a business. You're adding features to grow marketshare or scaling up to meet user demand, so it has a more direct correlation with the health of a business. It's less of a cost center, and more of an investment.