There are many reasons an individual might adopt few, some, most, or all of a religion's rules of behavior.
And there are a variety or reactions of individuals over time, from chaffing, deepening involvement, to abandonment.
There is also the need for a social organization to have a complex set of rules so that adherents can become more involved. These people then become the support and leaders of that group.
It might be Judaism - with arcane rules of kashrut - or bicycling, with arcana involving equipment, routes, clothing, deit, etc.
But these groups and religions only persist over decades if they can continually involve and reward a core group. Having a complex set of core rules is a very effective way of creating the core group.
With this perspective, you see that the point of restrictions and unique rites is to perpetuate the group - just as the point of eating is to stay alive, so that you can then eat the next day.
And, just as one person might rejoice at rain, while another complains, so do religious adherents have a variety of responses.