Trump being deplatformed, while having good reason, could have likely concerned cabinets and governments worldwide that they may as well "just in case". Also, having something like "10downingstreet@social.gov.uk" or "potus@social.whitehouse.gov" seems more legit then "10downingstreet@threads.net" or "potus@threads.net". It's a similar idea why they don't use gmail/outlook addresses

Keep in mind, I'm talking governments and media organisations. They could likely just ask an intern to do it for them lmao. The benefits outweigh the cost. Even plenty of tech nerds have personal instances.