Do lightweight wallets validate signatures? If not, why? I've learned that "some SPV clients simply don’t check signatures themselves at all": https://bitcoincore.org/en/2016/01/26/segwit-benefits/#efficiency-gains-when-not-verifying-signatures

I wonder if popular lightweight wallets (like Electrum) nowadays do signature checks? If not, why?
Some lightweight wallets do not check the signatures because checking the signature requires data from the previous transaction. However lightweight wallets generally will not have the previous transaction to fetch the data from and are thus unable to verify the signatures.