Check airman
It was always so as the average line captain isn't an instructor and it's not the time nor place to train a FO.
My first real crosswind landing I nearly stuffed the wing tip into the Tarmac.
When is the proper time for the FO to get the training experience?
You only have so much time with an instructor as a FO, and a similar amount of time when you upgrade to CA. The instructor can't expose you to everything. In the thousands of hours in-between, why not do some training/mentoring?
At my airline (US Regional), the FO is restricted for the first 100hr on type. Thereafter, both pilots operate to the same limits.
I've taken my aircraft to within a few knots of the demonstrated crosswind on multiple occasions, and I'm a more capable pilot after each experience.
Some CA's are better teachers than others, but your average line pilot is perfectly capable of providing instruction / guidance to new FO's.