and I don't think this number has become lower during the years passed since then. I think we can safely assume that hundreds of millions of people bet on sports each year.
I don't think you understand statistics and odds very well, else you would not have said that.
If the number of people betting goes up, then the odds of you winning will go down. That's statistics. So don't live in false hope.
Firstly, I think you misunderstood what I was trying to say in that post of mine. Secondly, indeed, I don't understand what are you trying to say here.
Say, I'm betting on a team A today, when the number of bettors is 1 million. Are you saying that tomorrow, if the number of bettors will be 10 million, the odds of me winning will go down? Do you think that the number of bettors affects the performance of the team A? Or else, how can my odds go down?
Most bookies will alter the spread to ensure the house remains profitable no matter what, even if 99% of all bettors bet on one side of a match, the bookie cannot lose money.
And they never will. But they don't have to alter anything for that, they will earn because of the house edge. If 99% of all bettors bet on one side of a match, and they happened to be winners, then the money of that 1%(minus the house edge) will be distributed between the 99%, and vice versa.
So, can you please explain, what did you mean by saying "Most bookies will alter the spread ..." ?