The company is not simply a magic mask I can put on and off at will; it is constrained by the laws of Japan and the United States, particularly with regards to taxes. Both countries are very lenient with regards to necessary business expenses (必須経費 over here). Neither particularly likes arbitrary money moving out of the company; that smacks of unreported income.

The company has books. All money into the company and out of the company is recorded on those books, in a fashion meeting various legal requirements of both countries. If I say "Donation" next to a line item and the NTA reviews it they'll say "Not allowed; adjust this item to be a distribution to yourself, pay income taxes on it, and don't do this again or we'll be very cross with you." If it says "Software license" the 99.999% case is "Seems reasonable" and the 0.001% case is "Random line-item audit: produce the documentation about this", to which I say "Here's an invoice" and they say "Alrighty then."

Sounds like an excuse to not donate

Again, I do not donate. I just send checks for thousands of dollars to OSS projects.