Because they are close source and not open source, this has a lot of meaning in the technical aspect in knowing what the source code is all about and can be verified, but when this becomes hidden, then such could be use for any unhealthy activities anytime in the future, if you noticed that trust wallet and metamask are the two wallets mostly used for altcoins and people now are mostly in use of metamask over trust wallet in many circumstances, you can decide to ask the bounty hunters.