do a little research before you spout off.
Yes the capability is there for about 55% of Americans to do it (as in technical capability for various reasons)
BUT for someone to actual watch/record/etc a three hour plus event that way?
BIG difference in taking a video off of you tube, etc and watching an NFL game on your computer.
I have streamed and will continue to stream all sports without any real effort whatsoever without a hiccup for at least the past 2-3 years. I think you're off-base in assuming that it takes much additional effort at all, especially considering the cost savings incentives of cutting the cord.
Beyond that, I think your #s are well off as well. The population of the US is far larger than the population of potential NFL viewers on a weekly basis. Think the number of streaming viewers is understated too, but I don't really have any way to quantify or estimate that.
Even if you assume your streaming estimates are accurate, 10M is 7% of an assumed 150M base (NFL fans only, which roughly half the population identifies as). With that 10M number growing each and every day, month, and year, it is a significant and almost certainly the largest contributing factor to the NFL ratings decline.
This is coming from someone who thinks the entire National Anthem protest issue is utterly ridiculous. I honestly just think this is common sense.