Why do some Christians want to believe that conversion is a life-rest button...

Why do some Christians want to believe that conversion is a life-rest button that erases the consequences of a person’s past actions?

Because for them, Christianity is not about Christ; it’s about finding yet another excuse to evade responsibility. If you bring that up, it touches a raw nerve in their conscious (see the comments below for examples).

Promoting the false “escape the consequences of your actions” version of Christianity to the spiritually naive and irresponsible is evil but also very lucrative. The church used to openly sell indulgences; now it’s more of a direct-to-consumer grift.