People are concerned about how much "ROI" they can get from investing in bitcoin compared to the alts. It's not about how cheap or expensive the price of bitcoin is.
Let's imagine when someone had 100 bucks to invest in bitcoin, and how long it needed for him to double his money: 1 year? 2 years? Don't forget that the bigger the market cap, the more difficult it is to increase. People thought bitcoin was too expensive, but this caused by they had limited money to spend, and If someone has $100k to invest, I think it is always worth it to invest in bitcoin.
You are right, people say bitcoin is expensive not because they don't have enough money to invest in it but they are comparing the "ROI" between bitcoin and altcoins. What they care about is the return they will make on their investment and it is clear that investing in bitcoin will not give better returns than altcoins. So most people will not want to invest in bitcoin and they give the excuse that it is too expensive.
When investing, people are usually concerned with the value of fiat and the rate of return they will receive based on fiat, not many investors care about the amount of bitcoin or the amount of altcoins they own . So bitcoin price has never been their concern.