But do you know why stellar doesn't have it's own wallet?

I use Ledger Nano S to store my stellars. There are others as well: https://www.stellar.org/lumens/wallets/

That's nice but those wallets are third party wallets in which they themselves didn't give guarantee

Those are the third party wallets they themselves promote on their website

I do not understand why "own" wallet is such a big thing. Wallet is usually just a safe keep for private keys.