WIY, there certainly is a percentage of people looking to excuse breaking halacha. But primarily, the people I know who went OTD did so because they didn’t find the evidence sufficient to believe.
You are also neglecting the Orthopraxz movement where people stay outwardly religious because they have too much to lose (wife, family etc).
I think people like to say things like “OTD just want to fulfill taivos” but for a large percentage that just isn’t true. I think it makes us feel better because it removes doubt that the people who no longer believe (as opposed to those looking for excuses) are correct. I think its an insecurity thing.