Verified emails provide a number of benefits that we felt outweighed any potential pain caused by having to go through this process.
As just one example:
Without a verified email if your account is compromised we need to manually verify you are the account owner through the Player Support team which means you aren't able to play for hours.
With verified emails we can make that process automated, allowing you to unlock your own account quickly and easily.
It also allows us to add more security features like multi factor authentication which will be coming soon(TM) so you can better protect your accounts.
For those of you worried about your personally identifying data, we do not share, sell or trade it for rare Pokémon, you can read the privacy policy here. Also as we announced a few months back, as part of the GDPR evaluation we have taken steps to better protect & encrypt player data that we store.
Email preferences for marketing mails are also separate so this doesn't mean you are suddenly going to start getting promotional mails or anything like that (unless you decide to opt in). In the future we plan to add a preferences center to make it a little easier to manage what types of emails you do or do not want to get from Riot.