What Cryptos are not available on metamask?

Could you elaborate on the cryptocurrencies that are not supported by MetaMask? As a leading cryptocurrency wallet, MetaMask has become a preferred choice for many crypto enthusiasts. However, given the vast landscape of digital currencies, it's natural to inquire about the limitations. So, are there any popular cryptocurrencies or tokens that MetaMask doesn't support? If so, could you provide a brief list or explanation of why these particular cryptos are not available? Understanding this aspect would help users make informed decisions when it comes to managing their digital assets.