system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do shady websites put numbers in their URLs?

You know like 36cashfromcomputer.com or 54studentloans.edu or whatever? At first I just assumed it was because the URL they wanted was already taken, but I've seen the same company use different URLs over time. Like they use it for a little while but for some reason they have to move on.

Edit: These were all really great answers so far. Thanks a lot.
gpt
There's two reasons usually:

1) They are either referral codes because basically people set up those sites as resellers of whatever product the site pushing.  They have to know who to pay.

or

2) They are for tracking purposes.  Like when you see a commercial and they say "click here and type PROMOCODE in the box!", it's so they can track where you saw the commercial so they know where their marketing money is generating customers.