Why did the majority of scholars consider usufructs as wealth, and what is the reason for usufructs and pure rights being excluded from their concept of wealth?

The difference between manfa'ah (utility/usufruct) and intifa' (usufruct/utilization):

Manfa'ah: These are rights that their owner can utilize themselves, or allow others to utilize, whether for compensation or without compensation. An example of this is renting houses.

Intifa': These are exclusive rights whose utilization is restricted to their owner only, and it is not permissible to allow others to utilize them. An example of this is marriage.

Al-Baquri clarified in his summary of differences that "by 'ownership of intifa', we mean that one directly utilizes it oneself only, whereas 'ownership of manfa'ah' is broader and more comprehensive, as one can utilize it oneself and allow others to utilize it for compensation, such as in leasing, or without compensation, such as in lending."

Examples of intifa': Residing in schools and mosques, and marriage, where the owner benefits from them only for themselves.

Examples of manfa'ah: Renting a house or borrowing it, where the renter or borrower can reside in it themselves or allow others to do so.

In the Kuwaiti Fiqh Encyclopedia: Intifa' is the right of the usufructuary to use and exploit an asset, and they are not allowed to rent it out or lend it to others. Manfa'ah is more general than intifa', because in manfa'ah, one can benefit from it oneself and allow others to do so, such as by lending it or renting it out.