Because it is fun.
I live in Brasil and we play real life football almost every week.
Due time constrain (work, family, etc) you can't do that hobby every day.
Even so almost every day we play FIFA on our work during the break time.
Most of us do that because it is really fun... we play in 4 people per match (2 people for each team).
There is a lot of things that makes the video game football different from the real life soccer:
- In real life your skills are well bad... you can be good but even so you don't train every day and you are way lower than professionals... and some guys are really bad (and loves to plays).
- In videogame you can play with others famous players (CR, Messi, Neymar, etc).
- In videogames you can to things you lack skill or your team lacks in real life.
- In real life you need a big time in your schedule (like 2-3 hours) because you need to go to a field way before start, prepare everything, start the play with friends, wash after the play, go back to home, etc.
- In videogames you can play with 5 minutes in your schedule.
They are complementary.
And videogames doesn't replace real life but real life doesn't replace videogames.
They are essentially different, fun and enjoyable experiences.
Why not both?
PS. GT7 already looks stunning even being cross-gen.