Email works best when people actively chose to hear from you. Bought lists and vague signups produce poor engagement, weak trust and, before long, deliverability problems that affect everyone else on the list too.
A smaller list of genuinely interested subscribers will outperform a large list of people who barely remember joining. It also costs less to send to, since most platforms charge by contact or by volume.
Mailbox providers now weigh engagement heavily when deciding placement. That makes a cold list actively harmful rather than merely useless: emailing 8,000 people who ignore you teaches the filters something unflattering, and the people who do want your email pay for it.