why is hip hop today such garbage?

When the focus is on image instead of music, the results are predictable.

Hip hop never left, there's tons of great rappers out there who don't "mumble" or dress the way you described and actually rap about real stuff. It sounds like you found a few mainstream rappers you don't like and couldn't be bothered looking anywhere else.

Here's 60+ recent rappers/groups you might actually like (not even including the many 90s/00s rappers who still make music to this day).

Kendrick Lamar

J. Cole

Denzel Curry

JID

Freddie Gibbs

Big KRIT

Joey Badass

Mick Jenkins

Saba

Vince Staples

Danny Brown

Benny the Butcher

Conway the Machine

Westside Gunn

ASAP Rocky

EarthGang

Tyler the Creator

Dave East

Smoke DZA

Kota the Friend

Flatbush Zombies

Run the Jewels

Action Bronson

Jay Rock

Schoolboy Q

Isaiah Rashad

JPEGMafia

Rapsody

Noname

Smino

Earl Sweatshirt

Cordae

Chance the Rapper

Aminé

Brockhampton

Maxo Kream

Bas

Lute

Ab-Soul

Reason

Nipsey Hussle (RIP)

Mac Miller (RIP too)

Logic

GoldLink

Big Sean

Cozz

Wale

Buddy

Westside Boogie

Joyner Lucas

King Los

Tobe Nwigwe

Elcamino

38 Spesh

Flee Lord

CJ Fly

Aaron May

Bishop Nehru

NF, Hopsin, Token, Dax (I'm not a fan of these 4 but you might dig their style)