Most jobs are not provided by SV companies or Microsoft. Most prople are not in a career that typically hires from across the country at their own expense. Paid travel is a luxury enjoyed by a small segment of job candidates.
Expanding the scope of discussion to all jobs is disingenuous. It's pretty clear this thread (not to mention this forum) is fairly software centric.
Regardless, companies across just about all industries that hire from remote talent pools will pay for travel (consulting, finance, government, NGOs, banking, accounting, manufacturing, insurance, you-name-it).
Whether or not a given company expands its talent search to include workers in distant locations is bound by several factors, none of which are unique to "SV and Microsoft".
A company would have to be pretty damn unique in order to justify having candidates pay for their own travel + lodging.