Wallet NET worth should not be confused with wallet balance.
Wallet NET worth is a sum of all the funds held in the wallet, denominated in one currency (you can choose the denomination currency in the dropdown menu).
Wallet net worth does not display your actual wallet balance.
It is subject to change either because of the change in the XRP market value or because of the change in market value of one of the other currencies held in the wallet.
Example
Wallet balances:
30 XRP
70 EUR
Example: If 1 XRP were currently worth 2 EUR
Wallet net worth in XRP: 30 XRP + 35 XRP (70 EUR if converted to XRP) = 65 XRP
Wallet net worth in EUR: 70 USD + 60 EUR (30 XRP if converted to EUR) = 130 EUR