Lost bitcoins aren't really counted as a donation to other bitcoin holders because once a coin is lost due to human error, it cannot be benefited by anyone anymore. Unless, you have mistakenly sent the bitcoin to an active user, then just consider it as a donation and an experience you should learn upon. Lost bitcoins and other coins are trapped in the blockchain which cannot be retrieved, therefore no one will be able to utilize it. Meanwhile, those coins that are held in an account and then the owner suddenly forgets the seedphrase or password can no longer be accessed too. There is a very slim chance of getting your account back once you've forgotten the important information that are needed for you to open your account. There are some people who offer such retrieval services but most of them are probably scams.

The lost coins and impossible to recover accounts with coins just contribute to the basic supply and demand law. The moment either or both aforementioned situation happen, the supply will be little and the demand will be big, resulting to higher price value of the coin. I think this is more on contributing to the community and position status rather than being a donation.

Losing a coin or forgetting the significant details are very much saddening. I encountered many scenarios about it and I know it is indeed heart-wrenching to the owner. It's really needed for us to be careful and mindful whenever we make any transaction to avoid these kinds of losses. We are responsible for our own funds, hence we should do everything that we can to protect it.