There are a lot of benefits of religion for people. There is the social and emotional support of belonging to a church group, stress relief from praying, answers to unanswered questions, financial support like food and shelter in times of need, etc.
Those people might be going to church for some of these benefits.
Because, some people don't have the same religion as they're family or friends. They don't want them to know who they really are, or what they really believe, so thier family and friends don't constantly try to convert them, shun them, or harass them for having a different religion.
Why does anyone fake anything? To look important? To fit in? To appear to be 'good'? To impress clients/friends (in certain parts of the country)? Out of a mistaken belief that going to church is all thats required?
The reasons many believe they are true Christians when they are not are many and varied. The false teaching that is so prevalent these days is certainly one reason. When churches eschew teaching sound doctrine, the end result will be congregants who do not know the truth of God's Word. Also, some believe their recitation of a prayer or responding to an "altar call"alone may have turned them into a Christian. Many believe their religious traditions, such as being baptized as an infant, secured a spot in Heaven for them, or that their plentiful good works alone have put them in good standing with God. And of course some believe church attendance alone guarantees salvation. The point is that many who profess to be Christians are not Christians at all. Yet they complacently remain convinced that all is well with their soul.
Some believe that once they are "saved" then they can pretty much do whatever and it won't matter to their salvation so they go to church to deal with their 'feeling' of guilt but they never use the power of the Gospel to change their every day life. They love the 'world' more than God