My pet theory is that its because these are "old guard" enterprises who have a strong presence in Washington. TikTok's blood is in the water, and all of these companies realize that they could get it at a substantial discount thanks to US Government intervention.
For a minute (or forever, whatever suits you), operate on the assumption that Trump is an idiot, who doesn't actually understand the modern business landscape, let alone the modern tech business landscape. He believes Boeing is one of the greatest companies in the world [1], the DoD has a huge contract with Microsoft, the federal government is also rife with Oracle contracts, these "traditional" companies are the ones that our government interacts with on a daily basis.
On the flip side, they just had an antitrust hearing with Big Tech (and while Microsoft was there, they didn't get nearly the heat that Apple, Google, and Facebook did; I wonder why). In fact, many of these companies, and others in SV, have publicly disavowed the administration; some had representatives on high profile advisory panels at the beginning of the administration, but many have left.
Who is left talking to Washington? The old guard companies, who have big contracts, big traditional names, personal contacts scattered around the federal government.
I don't believe this has anything to do with cohesion with these companies existing business models. Look at your confusion about who's coming forward, and then recognize that if the world doesn't make sense, something else is going on that you're missing. Oracle doesn't want to integrate TikTok with Oracle Cloud: They want to use their contacts in the government to acquire it at a serious discount, then bleed it dry to remake the investment. Microsoft feels like the only exception I've seen: While it still doesn't make sense for them, they at-least dabble in social networking, they'd probably run it into the ground, but it wouldn't be malicious.
[1] https://www.cnn.com/2020/03/17/business/boeing-bailout-trump...