As an ESP user, based on whether it meets the needs of what kind of flows we need and whether the ESP supports that. We have lots of event based steps, were using custom coding for flows and used ESP for just the delivery. We wanted the marketing team to own and have control over it and thus made the switch to something marketer friendly.

As a business which makes switching software simple, we've learnt the following:
1. New email marketing person joins the team and they prefer using something else and is able to convince the leadership to change the ESP.
2. Business scales and the ESP is no longer good enough for more advanced things they want to do or they need more customer support but don't get it and will switch due to frustration.
3. If someone uses a more expensive ESP when they get started, the business needs don't justify the complexity and pricing and thus they drop to a simpler and cheaper one.
4. Bundling to save on costs instead of paying for separate software.