Why are people content with two children these days?

Rich people probably wouldn't be rich if they had a big family....? I think I want to stop at 2 kids because it is more convenient to fit in a home or car, two parents (one for each kid), I have two hands (one for each kid). Having only 2 kids means that we can provide more for the kids that we do have such as holidays for example, we could easily afford private education if necessary for two kids rather than 4. I just feel that having 2 kids is better for them and for us for a few reasons. They will also get more attention this way. I don't think it's selfish at all, how can it be if we stop at 2 for the benefit of the two children we already have?