Usually, to trigger any kind of anti-trust law, you need to have massive market share. In this case, for example, Reddit almost certainly hasn't committed any antitrust violations, because they're a relatively minor player in their market.
Similarly, if you start a vacuum cleaner company, you can make whatever exclusive deals you want. But if you control 80% of the market for vacuum cleaners, then you might need to be more careful about leveraging your market share in unfair ways.
If a company is part of a robust, competitive market (like Reddit), it's usually wiser to let customers vote with their wallets, and leave the government out of it. If a company becomes massively dominant (like Google or TicketMaster), and if it starts pushing exclusive contracts, it's much harder for customers to switch away.
Similarly, if you start a vacuum cleaner company, you can make whatever exclusive deals you want. But if you control 80% of the market for vacuum cleaners, then you might need to be more careful about leveraging your market share in unfair ways.
If a company is part of a robust, competitive market (like Reddit), it's usually wiser to let customers vote with their wallets, and leave the government out of it. If a company becomes massively dominant (like Google or TicketMaster), and if it starts pushing exclusive contracts, it's much harder for customers to switch away.