I don't think it has been true for every alt, but it definitely has been true for a lot of them. As far as the future, who knows. There may be a few alts that have a viable purpose but a lot of them only have the purpose of scamming someone to enrich themselves.
Yes, there are a lot of useless altcoins, created just for the purpose of scamming and enriching themselves. But it's not all bad, there are a lot of altcoins that have grown alongside bitcoin over the years, and they are still working tirelessly to continue to grow and bring more benefits.
Agreed that most altcoins are centralized, but we cannot deny their efforts just because of that while their purpose is completely different from bitcoin. Each coin has a different role and purpose, we cannot deny them just because they do not follow the path of bitcoin.
It is really biased when we criticize all altcoins and assume that all of them are useless and not worth investing in long term.