In most cases, it's free to start using a crypto wallet. However, everyone must eat and there is no free lunch. If something is free, then you are the product. Crypto wallets are free to push adoption. But there will always be some functionality that will allow crypto wallets to earn money. For example: >> Metamask earn a fee if you use their on-ramp or swap function. >> Phantom wallets earns a fee if you use their staking wallet