What Do Sweepstakes Companies Do With Your Email?
Your email address is the price of the entry. That is not a scandal and it is not hidden: it is written in the rules and the privacy policy, and understanding it is the difference between a manageable inbox and an unusable one.
The company running it mails you
The company running it adds you to its marketing list and sends offers, which is the entire commercial reason the giveaway exists. Legitimate senders must include a working unsubscribe link and honour it, which US law requires under CAN-SPAM.
Sharing with partners
Some entry forms include a consent line permitting the company running it to share your details with marketing partners, and that is where a single entry can turn into mail from companies you never heard of. The line is usually a checkbox or a sentence above the submit button, and it is worth the five seconds.
The practical setup
Use one address for entries and filter it into its own folder rather than unsubscribing from everything, because prize notifications arrive through the same channel and often go to spam. Do not use a work address, and never give a phone number where the form does not require one.
What a company never needs
A Social Security number is required only at the point of claiming a prize of $600 or more, for the tax form, and never to enter. Nobody needs your banking password or card number at any stage.