Why are presidential transitions paid for by donations?

I’ve been reading about Trump’s taking donations from anonymous donors for his transition efforts. Here’s one:

https://www.nytimes.com/2024/11/24/us/politics/donald-trump-2024-campaign-transition.html

Here’s a two-paragraph excerpt from that article:

The current Trump transition, like its predecessors, is set up as a “dark money” nonprofit. Those groups typically do not have to disclose their donors, even to the Internal Revenue Service. But unlike Mr. Trump’s team this year, earlier transitions accepted financial support from the General Services Administration, which oversees much of the transition process. In exchange for that federal money, they agreed to conditions that other dark-money nonprofits do not have to follow, like capping individual contributions at $5,000 and disclosing the names of their donors.

When Barack Obama won the presidency in 2008, his transition raised $4.5 million while restricting donations to a maximum of $5,000, and pledging to refuse money from corporations, labor unions, political action committees, lobbyists and registered foreign agents. Nearly 60,000 people contributed, with an average donation of about $75.

(End of excerpt.)

Why is this necessary business the goal of fund-raising that lets people gain favors or purchase influence? Or why would anyone donate if they don’t gain from it somehow? Why doesn’t the government cover these expenses? What’s really going on with this?