Because it is not certain that the number is inaccurate. I posted a photo of the World Encyclopedia above…as you can see, it takes two very large volumes to contain all of the data.
Since someone has gone to a lot of trouble to document his research, I think we should not dismiss it lightly.
The number of Protestant denominations is VERY large, considerably more than the ONE that Jesus promised to build in Matthew 16:18, and while 30,000 may be a bit of a projection based upon the research referenced, it is a very good projection backed by real research.
Regardless of the actual number (and it’s well into the thousands no matter how you count them, IMO), the problem of the ongoing division among Protestant communities flummoxes Protestants - I don’t recall ever hearing a coherent response to this - other than those fundamentalists who take the “I can’t help it if everyone else is wrong” approach.
Nothing reveals the absurdity of sola scriptura better than the scandal of Protestant denominationalism.