The emails sent by your $5 VPS wouldn't stand a chance of actually being delivered to people's Gmail or Outlook mailboxes. Whereas SES actually works.
Also, it is incredibly easy to ask AWS support to increase the limit. A startup I worked with had only thousands of users; we told AWS about it and they gave us 5 million emails per 24 hours.
By all reports of people who have set up their own mail server lately, just having SPF and DKIM set up still won’t cut it for delivery to the major mail providers these days.
I run my own email server, with no spam filter, and inspect where every spam comes from. I get a lot of spam from random shitty providers, but none from major VPS providers (Scaleway, Hetzner, Linode, Digital Ocean, ...) with the exception of OVH.
I do however get spam from Amazon SES a couple of times a month.
Also, it is incredibly easy to ask AWS support to increase the limit. A startup I worked with had only thousands of users; we told AWS about it and they gave us 5 million emails per 24 hours.