Re: Question is...
There are also network effects for large ad businesses. Your ads carry a big bonus if you can guarantee that at least X% of the population see them. For that reason, when you have a large ad business, you have a strong disincentive to offer ad-free tiers. The reason is that when people switch to the ad-free tier, you not only lose the ad revenue, but you can even charge less for ads, because advertisers know that their ads is reaching only part of the population so they are less valuable.