They're separate products. You can buy one, the other, both or neither. Nobody is forcing you to buy anything. Buy it if it is worth it to you. Don't if it is not.
Let's say that you buy both. And all of both. That might be $2000 if you're not smart about how you do it.
You've been able to play 5E since June 2014. Let's say you play 4 hours a week on average since release of the game. We won't count any of the time you spent happily thinking about the game when you were not playing, because obviously we don't draw any additional pleasure form thinking about the game, visiting free message boards about the game, preparing for games, etc... We'll just focus on that roughly 1000 hours at the table estimated for 5E that people with a regular weekly game might have enjoyed. YOU'RE PAYING $2 per hour.
Oh, wait, you only play half that much? $4 per hour if you bought everything, and were not wise about it.
When it comes to spending money on entertainment, RPGs are some of the best options for maximizing fun and minimizing cost. You can play a really fun PC for $0 with free materials! Heck, you can use a dice app and not even buy dice!
I get that not everybody can afford $2000 for books and virtual content. I get that there can be other costs. I also know that one of the best DMs I have ever met never spent a penny on the game in 30 years of play (RIP, Bud). But, if you want to argue that they're ripping you off.... well, it just doesn't add up.