> Imagine being a 'frontend developer' who can only use squarespace.

More likely: Imagine being a 'frontend developer' who can only use React.

Seems horribly limiting regardless of how we slice it.

It's sad because it's a reality for many

There are people who are trained and know mainly Wordpress, so not a surprise. However, if they can transition to a second product, they will be able to generalize to a n-th as well.

IDK, I used to worked with "Drupal consultants" who barely knew PHP. They delivered the sites they were asked to, usually on time and within budget.

Drupal was the only accessible door to me to this entire industry in 2010, with no CS knowledge or available mentors. I was one of those people and I barely fed my family, and I eventually learned PHP, JS, the hosting stack, automating the hosting stack, Varnish and HAProxy, Linux sysadmin, how the internet works, and a decade of topics since.

We all need a door into this stuff, a place to be dropped in to start putting it together. Maybe the OP’s sister in law is totally out of luck, or maybe she’s now got a few of the hundreds of tools she’s going to need to build out a career. Luckily she has a brother in law in the industry, hopefully he’s the helpful type.

And they could migrate to WordPress if all theirs customers had to migrate.