In the modern day and age where Christian religious practices, even among the faithful, are quite lapse then it's less the case.
But that was their intention, and it was a form of soft control where they made it feel like a choice (but was frowned upon if you didn't so was upheld socially). Your behaviour and your routine will be affected by the requirements of religious festivals, which is a form of indoctrination. You're not going to be happy if you give something up for 40 days and someone tells you it doesn't make the blindest bit of difference.
It's why I think in the current climate that Muslims are far more likely to be angered than Christians with comments about their religion. Even slightly lapse Muslims will adhere to things like Ramadan quite strictly whereas I can't think of many people who would consider themselves as believers in God and raised in a Christian tradition who adhere to Lent. I think quite a few wouldn't even remember when Lent was, or that if even existed, without being reminded.
You're doing things that are difficult and a burden so you're invested in upholding them, and of course you're going to react if it's suggested you're putting up with it for no reason.