Surprisingly enough this is not the case, at least in Europe. I sign up for the majority of websites/apps using my primary email but make an effort to go to the account settings and immediately opt-out of any BS emails/notifications.

Every once in a while something slips through (which I make sure to email their DPO as per the GDPR and ask what's going on, and they make up an excuse on how a misconfiguration/etc resulted in me getting spammed, but at least it puts downwards pressure on this behavior), but it's manageable - my inbox is clean and averaged over a few years I get a spam maybe once a month.