I’m wondering whether it’s more of an issue of the Parliamentary standards asking a very narrow question e.g. did Boris mislead parliament and they can get away with just handing over the non incriminating stuff so if a few bits go missing or accidentally not sent it it isn’t a big deal. And it specifically focuses on Boris not everybody working in the CO/ no 10. Also he’s no longer PM, is barely in the country let alone Westminster and lying to parliament is now a fairly accepted weekly event.
Covid inquiry has a huge remit. It’s going to need everything that’s official. Which presumably is big problem if you are daft enough to use personal WhatsApp accounts to have official policy discussions and are also stupid enough to use that same account to have all the discussions about dodgy illegal dealings and organise your illegal lockdown work parties. It’s also led by a judge who it seems does not want her legacy being the head of a dodgy covid inquiry. Nor, I’d imagine, would she ignore anything illegal but not to do with covid that landed in front of her as part of official government records.