Do you mean that the number of exchanges will continue to grow, so that we can buy Bitcoin on any exchange we want?
Actually we don't need too many exchanges to invest in crypto. What we have prepared is a list of local exchanges where we make deposits and withdrawals, then international exchanges where we trade.
Actually, it doesn't matter how many exchanges you need if you just want to buy Bitcoin. But only trusted exchanges are needed by everyone to buy whatever everyone wants and that includes Bitcoin, because why are there so many exchanges but the trusted ones are only one or two exchanges that are convincing to use, be it local exchanges or exchanges international.
But why also the number of exchanges continues to grow? Because the number of crypto developed also continues to grow. In general, everyone likes Bitcoin, but not everyone invests in Bitcoin. So the coins that are liked by someone are only available on certain exchanges.
And it's true that not everyone invests in Bitcoin because it's caused by two things, first as you said where someone only likes certain coins on certain exchanges other than Bitcoin. The second is because the abilities possessed by each person are different so that each person tends to choose investments in different coins based on the abilities they have at any given time.