Email is in a funny space. Spf showed up. And although it meant some political fights when people expected to send email from anywhere, it was free to run in the dollar sense. Same with dkim.
Dmarc is increasingly required to get past spam filters. And doing dmarc properly requires a reporting service. Either you run servers or use a hosted service like the one that created this page. That's fine for some business, but putting a cost on dmarc reporting and then making dmarc a heavy signal in spam filters is a huge pain for some scenarios.
It's not highly expensive, but on non monetized side projects it can frustrating how how much the internet expects you to have dmarc on every domain now.
This is incorrect.
DMARC requires nothing but an email address to send reporting to. It costs nothing to implement and there are open source [0] solutions out there if you want to monitor the reporting being sent.
And to clarify - the reporting you're getting back from a DMARC is either an aggregate or a forensic report. There aren't many email providers that actually send forensic reporting anymore, the 99% of reports you'll get are aggregate in nature.
And finally, remember that if you don't have a policy of "REJECT" set on your domains, DMARC isn't doing you a whole lot of good.