It's likely only recognized in Northern Ireland and Wales because they'd already supresed Gaelic out of the Scots. England itself doesn't need English listed as a language because the ruling class never tried to stamp another language/culture out of Englad they way have Scotland, Ireland, or Wales.
Doesn't sound right to me. As someone living in Scotland, my understanding is that the Scottish Government recognises 4 official languages: Scots, English, Gaelic, and BSL.
Loads of stuff in the UK is not set into law but rather into custom iirc. So instead of "because the law says so" they have a bunch of "because we've always done it this way".
Unfortunately we are fighting against that effect too. Thankfully it's not as effective over here. A lot of our customs and culture are deep rooted, historically. This makes it a lot harder to overturn, without creating problematic ripples. It's not stopping them trying however.
As the saying goes. In America, 200 years is old, in England, 200 miles is far. A lot of our customs have been shaken out and tested over the centuries. They still exist because they both work and are hard to dislodge. America's government is a lot younger, and was made as a whole. This leaves it a lot more brittle, and so easier to break.
A good addendum to this is that the recognition of Irish as an official language in Northern Ireland only happened last year (may, 2022) with the passing of the The Identity and Language (Northern Ireland) Bill
I'd known that about the US, but always assumed that England had English as the official language.
Mind you, the aristocracy and royalty spoke French for 200 years so I'm wondering whether English, or French come to that, was ever the official language.
It's set by custom, rather than law. Languages drift and change. The church used to only use the Latin Bible. This left it inaccessible to most people.
Which version of English should have been locked in, by law? Latin? Old English? Middle English? International English?
The closest we came was "Queen's English". This was a semi standardised language and accent. It was mostly done to allow rich governors etc to not have issues talking to their staff. For reference, the BBC news was mostly done in Queen's English for a long time. It was designed to be clear and distinct, and so excellent for radio news (as well as talking in the court, or ordering your native servants around). While it sounds formal and stilted, it's very understandable for everyone. If you've tried to have a conversation with someone with a strong UK accent, you'll understand the importance.
FYI, 'pirate talk' is actually mostly a Cornish accent. Add to that Scottish, Scouse, and London Cockney and you'll understand why a common reference is useful.