You go with Mailchimp (or equivalent) for newsletters because they give you the subscription form, handle email verification, unsubscriptions, GDPR mentions eve

You go with Mailchimp (or equivalent) for newsletters because they give you the subscription form, handle email verification, unsubscriptions, GDPR mentions everywhere, provide useful stats and notifications, segmentation and targeting… Getting email delivered is indeed really hard, especially if you send thousands of emails, but building all these other features is insanely time consuming. The cost of Mailchimp is negligible in comparison. Same reason why companies use Sendgrid for marketing campaigns.