And many things have been done, including Windows telling you in bold red letters that this software is dangerous if it wasn't signed by a trusted signer with lots of installs.

And why are those not sufficient for Android?

This is not a theoretical issue. It’s a major problem is several countries, the governments are getting involved.

Yes, but governments are getting involved because governments always like increasing control and reducing freedom; the "major problem" is merely a pretext.

People are loosing their life savings

If you need to sacrifice your freedom for a little bit of security, then you deserve neither. It's true with this too.

Most rules/laws don't actually stop problems, they just hide them.

Are the governments also coercing Microsoft to restrict Windows users to the Windows app store?

No. In the impacted nations the issue is with the (vast) majority of people who only own an android phone.