If provider X provides a very limited (or no) quota for regular internet traffic, and provides access to sponsored zero-rated services - then this inhibits competition, and (depending on how agressively it's implmented) can inhibit free speech.
This has been seen seen in some countries such as India where facebook.com was zero-rated traffic, and data prices for regular internet access were extremely high.
It's also seen today in Australia where Apple Music, Spotify and Google Play Music services are zero-rated traffic on certain mobile (cellular) plans - many of these plans also have zero-rated access to various popular social media platforms too (facebook, instagram, etc) - and data quotas are generally fairly limited (2-10GB/month is typical for mid-range plans). A competitor to these services is going to have a very hard time entering the market, since their customers will all have the data usage come out of their regular quota.
Continuing with Australia - Most ISPs provide zero-rated access to Netflix (or provide 'unlimited' quota). Telstra does not zero-rate Netflix traffic, but they do zero-rate Foxtel and their own movie/tv services. At the same time, having rather low data quotas.
So those who're stuck with Telstra (eg because they live in an apartment/development that is a Telstra-exclusive estate, or just because they're on a 24-36 month contract, having been unaware of the problems) - are unable to use Netflix.