Everyone sells your data. Yes literally everyone. Even the ones that promise they won't. (The mulligan is in the EULA you're forced to agree to)

You put your name and email into any website ever, then you're out there. On untold numbers of lists.

Ordered a pizza online? They got your number, name, email, and location. And it was sold before you ordered that pizza.

Ever bought a single item on Amazon? Same thing.

Insurance quote online? Sold to a data broker.

If you wanna sleep poorly for the next week? Take a deep dive into just how much of the economy runs on that data. Data with no protections. Freely traded on the open market. You can even buy your own data. Don't do it. It'll scare you to death. But you can do it.

I’d be interested in learning more on how to trace my data, beyond asking the telemarketers where they got it.

So I get zero calls now. I spent a year not answering my phone (helps I work nights) but when I was able to answer I just sent it to my Google assistant every single time. They always hang up before it finishes the introduction. I haven't received a spam call in two and a half years now.