many( especially regulators ) believe it to be mainly due to the lack of legal rights.
This is one of the reasons why,
Since crypto is not being controlled by the government, they see it as a lack of legal rights. Even if it is considered as money, online money, or an intangible asset that can be used to purchase or do transactions, as long as they don't have the right to control or regulate cryptocurrency, they will not consider it as an asset.
Mostly people think about an asset is that being legalized by the government and is supported by it but for me, as long as it has a good value that can be very beneficial in the future, then it can be considered as an asset. Hopefully once cryptos will become a mainstream and starts gaining even local adoptions from the government, people will definitely start seeing it as a good asset.