I think it's harder to pull the trigger and launch once you've taken so long (years) to work on a project. You're a lot more invested in the success or failure,

I think it's harder to pull the trigger and launch once you've taken so long (years) to work on a project. You're a lot more invested in the success or failure, so you take a perfectionist view of the project which is a view that often leads to procrastination. When you're only spending ~2 months developing a bare-bones MVP, it becomes easier to just launch the thing and be less attached to the ultimate outcome. This is just my personal experience, I've worked on both types of projects and I vastly prefer the ones that take only 1-2 months to validate.