If btc goes to 100k it will "only" have (more or less) doubled from its ATH.
From there it will need to rise another 100k in order to double again. I don't say this is not a good investment, but first of all crypto owners are spoiled, until up to now we were used to 10-fold, 20-fold + increases, so doubling the money has not been really special.
But this smaller reward ratio is paired with a much bigger risk ratio, since btc's swings in a correction period will also get bigger.
For hodlers who are in from the very beginning, it won't matter much probably, but where will btc find new buyers when it has reached 100k and needs to go up another 100k in order to double again in price?
And the fear of FOMO will also become smaller, as people will at one point accept, that the train has left the station.
Of course, should btc show convincing signs that it could reach 1 Million very quickly, then the whole picture changes.
It's a very valid point and all this investment money pouring in might eventually wake up to this fact - the smart money will start chasing other coins which can grow hundreds of percent in very short timescales (like Dogecoin showed us). For Bitcoin to reach a value of $1,000,000 actually seems a bit ridiculous when you consider it doesn't produce anything, costs huge amounts of energy to create and the transaction fees tend to scale up along with the price. At that price it would have a market capitalization of $21 trillion, the is the same amount as the whole US government owes in debt and even the New York Stock Exchange (the largest in the USA) is altogether worth roughly $26 trillion. Maybe this realization will slowly deflate the Bitcoin bubble, but I have a feeling a lot of average consumers who are still clueless about the cryptocurrency space will always gravitate towards the most well known "brand".