This is exactly why. They see TT as the "new" form of social media, since everyone is sick of FB-style feeds and profiles, and want a piece of the action. TT's growth and young userbase demonstrates pretty clearly that traditional social media isn't cool anymore.
I guess when you are bidding against other people, the highest bidder wins. That means you have to, in a way, overpay for the product, and reap some special synergy bonus that other buyers can't get. This is what is missing to me, I can't see how owning a social media app enhances the rest of the business for either of Microsoft, Oracle, or indeed Walmart.
The problem with trying to buy a business like TikTok at its prime is that it's trying to buy "cool". It's the most perishable commodity imaginable.
Let's assume that you manage to skate by the initial purchase process intact-- that the audience doesn't revolt en masse and say "I don't want to be associated with Walmart/Microsoft/Oracle". In a way, a unfamiliar foreign owner has a bit of mystique-- everyone in the target demographic has been in a Walmart or dealt with a Windows PC, so those brands have baggage already, whereas this was most people's first contact with ByteDance.
A lot of the potential 'synergy bonus' opportunities have to be intentionally slow-walked to avoid setting off the audience's spider-sense. Push "buy goods via TikTok" too hard, or push the wrong ad inventory because it's all you have, and users will walk away.