> In the end what changed is that e-mail based marketing was on the decline, with other mediums taking over.
FWIW this is completely incorrect. Over the past 2 years other marketing channels have skyrocketed in cost (eg FB ads) and most brands/companies are now investing heavily into email marketing. It's a significant growth industry right now, more so than at any time since I've been involved with email marketing (since ~2010).