There are a ton of citizens who would benefit from college but can't afford to go. I struggle to see the utility in discriminating against your own poverty-stricken countrymen in this. What's the real motivation?
Real motivation is he wants to help DACAs. Does this mean to you he doesn't care about other people's life. Or you are saying it is unethical for him to donate to DACA unless he solves everyone's problem otherwise he should do none of that? This is a quite reactionary world view that doesn't really help you.
There's an argument to be had on the lasting consequences of uneven help, or even whether billionaire opportunism is net good for society, but yours doesn't look like a good starting point because it appears to demand perfect help or no help.
Perhaps people are susceptible to recency and trendiness; and perhaps Jeff Bezos also sees opportunistic political timing; and perhaps Jeff Bezos thinks that the uncertain future of hundreds of thousands is a bit tragic; or perhaps the nature of help is naturally uneven, because we are best equipped to help the few issues in front of us.
But your discussion narrowly starts with the character of specifically one Jeff Bezos.
Many Americans (myself included) believe most DACA recipients deserve citizenship, as they were brought to the U.S. illegally by their parents while still very young through no fault of their own. DACA recipients often consider themselves American, having grown up in U.S. public schools speaking American English and immersed in American culture. As young adults, the DACA program allowed them to pay taxes, hold down a job, pursue an education, and generally keep on being Americans.
In the view of DACA recipients as unfairly disadvantaged Americans, Jeff Bezos is indeed helping his own countrymen.