Some of them do.
But, I think it is mostly the female part of the couples whose skills/qualifications are more difficult to translate. Many of the men who are quite happy here are builders, and they have not had problems integrating with the work force.
In my BILs situation, his dp has been living here much longer and she has qualified in Britain. Bil hasnt, and his work experience in Poland does not count for much. This means she has a good job (for a Polish company), and he doesnt. He is keen to return. He thought life would be great in Britain, and 2 years on he is quite disillusioned. She has friends and family here, as well as a good job, so it is tricky. He is considering resigning his job because child care fees are more than his net income. This will make him a stay at home dad.
My husbands aunt also worked for a Polish company, and hardly ever had to speak English in work. Being part of the Polish community, her English is still pretty basic after over 30 years here. They also only watch Polish news, and have Polish tv, subscribe to Polish newspapers, shop in Polish small shops, complemented by the old trip to Tesco. Her husband never found work here, and he has been "keeping house", cooking and cleaning and raising the kids.
It seems to me that "universal skills" like plumbing and building where you dont need to come into contact with the public is easier than if you have to communicate a lot with the public. Also, it is easier to find work if you work in, and serve, your own community. In most cases they dont get to use their skills and qualifications, but start from scratch as cleaners, child carers, often while they try to get new British qualifications. Be it beauty therapy or nursing, etc.
Bear in mind I am talking from my personal empirical experience. You know, it is like a box, you can only look at it from certain angles, and not see all the 6 sides and the inside at once. This is the truth from what I have experienced, but I am not speaking for all the Poles in Britain, only those I know!
Regards to qualifications, my UK qualifications were not recognized in Norway, even if they were from a top of the range well known University. I had to send off all my uni related paperwork to an organization that verified that these were actual qualifications. Despite the historical content in my degrees, I was still not accepted into a teacher training course here, due to the differences in the syllabus between Norway and the UK. So, it is not just that Polish qualifications are not recognized in Britain, I think it is across the board, and something OP needs to verify.
OP why dont you ask your Polish friends that has already moved to the UK what their experience is?