I have always been perplexed by the vast variation of Pesach cleaning practices. On the one hand I have seen notes of shiurim by respected rabbis who say that virtually the only real work to be done is to prepare the kitchen / pantry for Pesach... and even in the kitchen, only what you are going to actually use for food during Pesach (e.g. if the oven will not be used, it need not be cleaned at all). As for the rest of the house, if you want to close off a room for Pesach, you don't need to clean it at all and if you do want to use the room, you just need to make sure there are no large pieces of chometz in there and sweep the floor.
On the other hand there are people that spend the whole day scrubbing an oven they are not going to use for Pesach, spend multiple hours cleaning each bedroom, paint the walls in the kitchen and dining room, spend hours scrubbing chairs and tables, etc.
To me, these seem like almost different religions. How do I reconcile this?
Related question: Is it true that the first (i.e. easy) scenario is based on what is written in the halacha, and the second (i.e. very hard) is based on custom?
And if so (that the second is custom), couldn't it be considered a sin, since you are thereby taking away so much time that could be used for doing things that are really mitzvos and also the fact that you are implying to others (including your children) that this is the halacha, when in fact it is not?