Because they are not usually watching the game in the actual sanctuary. Obviously your experience with churches is slim, but fellowship halls are a part of the church-going experience. After the worship service is complete, it is not uncommon for the congregation to meet for lunch and continue the fellowship in the other ares of the church. This can include anything recreational that fosters a Christian way of life. I don't understand how you can equate sporting events to blasphemy.
I distinctly remember being a senior in high school and attending "5th Quarter" at the church on Friday nights after the high school football games were over. We'd make a habit of ordering loads of pizza, open up the basketball courts, turn on the big screens, and hold a prayer devotional before the festivities began. Nothing uncommon about that at least where I'm from in the US.