The main driver is talent base, ease of operations, and time zone overlaps.
The true value of offshoring comes from being able to essentially run 24/7 operations across a couple countries that have a strong talent base and relatively easy operations for us as a company (easy to fire, easy to hire, tax holidays, etc).
This is why Israel, India, Ireland, and parts of Eastern Europe like Romania, Poland, Belarus, and Ukraine became popular for software outsourcing.
The reason UK is a base is because UK business law is extremely thorough and any flavor of contract dispute has been litigated multiple times in the UK.
This means it's easier for me to manage operations all over the EFTA and EU via the EU-UK TCA.
The English factor is a massive plus as well because that is the global language of commerce - not French or German. This is why Netherlands tries to treat English as a first class language similar to Dutch, because that is critical for businesses.
Not sure about the rest but it's definitely not easy to fire in Romania at all, and workers there get a lot of mandatory legal benefits like generous sick and parental leave. Unless you hire them B-2-B, which is quite common for high wage outsourcing jobs, then yeah.
This is what my previous employer did
That another business is liable to pay them
I think the accent has as much to do with it as anything. Americans are culturally wired to overestimate someone with even a mildly posh British accent.