Altcoins especially these failed altcoins that died are not failed experiments, but they're successful scam attempts from those founders, developers. They are richer by developments and launches of these altcoin projects, but investors failed and lost money.
Both kinds of coins exist. Above all the older altcoins have often some experimental components, but that doesn't guarantee their success so several are near-dead.
What I meant is that 97-99% of the coins are "at least" failed experiments, but they can also be ponzis or scams.
We could build a kind of "altcoin tier system" with the following tiers:
A) Decentralized & successful (example: Monero) - no premine, preferrably PoW. Of course, Bitcoin would be something like "tier A+++".
B) Semi-centralized & successful (example: Ethereum) - had a premine benefitting the developer team, but the general the inner workings are relatively decentralized and they have a working ecosystem.
C) Decentralized & low success (examples: Feathercoin, Navcoin) - like tier A, but they weren't able to build up an ecosystem, so they tend to continuously lose value or stagnate.
D) Semi-centralized & low success (example: Nxt) - like tier B, but weren't able to build up an ecosystem, so they tend to continuously lose value or stagnate.
E1) Company coins (example: BNB) - are not really cryptocurrencies, but a value similar to a security as they depend almost 100% on the operating company
E2) Memecoins & short-term fads which were able to get some community support, but will also very likely eventually disappear.
We have at most 10 tier-A coins and 30-50 tier-B coins which are those interesting for mainstream altcoin investors.
Tiers C and D can in theory be still "valuable" and even can see some spikes, can be interesting for investors who like extreme risk. They're making up most of the top 1000 coins. There should not be more than 2000 coins of these five categories. Tier E, the company coins and memecoins, are a special case. Can be interesting for those who like to invest in penny stocks.
Now we have 20-30k or millions (according to CMC) of F-tiers where a loss for investors is almost guaranteed:
F1) Centralized/semi-centralized, still not dead, but extremely high fail potential. Their main development team disappeared, only some stubborn bagholders keep them alive
F2) Decentralized & failed (example: GeistGeld) - like tier A, but failed completely (dead, no exchange listing, or 51% attacked)
F3) centralized tokens and memecoins without any community & other short-term fads (this does NOT include coins like Doge or Shiba Inu)
F4) outright Ponzis & Scams
The "failed experiments" are tiers F1, F2 and F3, they tend to live for a long time due to the stubborn bagholders (exception: if they are successfully attacked), but they will very likely never recover. F3 and F4 are often manipulated and thus if you just ride the pump you can even make profit, but the probability is extremely low.