What these people are really saying is that it's not really bad enough on Reddit for them to migrate.
And you know what? Fair enough, that's a perfectly valid position to take, and we should respect that descision. Not everyone sees a third party app as all that necessary, and many are happy to scroll through promoted posts. It's not for other people to decide how you get to enjoy a product, after all.
Of course, many of us who have left have clued in that Reddit is not the product, Reddit is a cage to hold the product: Redditors; that the user experience on Reddit will only continue to decline as it inevitably does with the enshitification business model. Meanwhile Lemmy will continue to improve.
You can't save people from themselves. Some people are so entrenched they will stay to the bitter end. The cost benefit of jumping ship from one platform to another is going to be different for everyone, it's going to change as Reddit pushes monetisation and community projects focus on features to attract users, and you have to accept that.