there are 3.8m EU citizens in ONE country, but there are only 1.3m UK citizens spread between the rest of the EU27. There is nothing xenophobic in stating that the UK is far more attractive to foreign migration than rEU is to UK citizens -
Don't forget that many more UK citizens have emigrated to non-EU anglophone countries than to the EU.
It's more complicated than you are suggesting. Yes, the UK has been a popular destination for EU migrants, because relative to many other EU countries it has had more job opportunities, partly because of a more dynamic job market and partly because the UK education system has failed to train enough young people in occupations with skills shortages.
Language is also a big factor. Most students across the EU learn English: it's often compulsory to take a MFL until school leaving age (and beyond) and English is usually the MFL of choice. In the UK, OTOH, very few students leave school with functional skills in a foreign language. This drastically limits job opportunities in the EU27 - where I live in France very few British migrants are formally employed, because most don't have the language skills to work in a French-speaking environment. The majority seem to have small businesses catering for other English speakers (gîtes, odd jobs, building work, estate agency etc).
It is also probable that the numbers are wrong. We don't really know how many EU27 citizens are in the UK, and the estimates of UK in EU are even more problematic, because so many fly under the radar and remain theoretically UK resident, maintaining a property and paying taxes in the UK and relying on an EHIC.