Previous versions of Windows only permitted drive encryption in their premium tiers, and it seems like the current one possibly requires a TPM chip for it, so a lot of hardware won’t even support it. So basically greed or greed.
For what it’s worth it’s not always a default with Linux installations either. There’s a usually minor performance hit, though I can’t say it ever bothered me. Personally I have less fear of bad actors obtaining physical access than I do myself breaking something catastrophically and losing my access, so I don’t use it now.
There will be some additional time and resources required to read and write encrypted data, even if minor.