Ohh good question!!

A bunch of reasons so I'll just throw some general bullet points at you in no particular order hahaha

~Chichi understands him and he understands her

~I find it really sweet that our free-spirit-never-stayed-in-one-place-very-long lug of a warrior settled down and chose to have a family. Sometimes he has to leave them and it takes him a while, but he always comes home to them

~Goku thinks about Chichi a lot. Goku-is-Captain-Ginyu "what's chichi gonna think about this??" and telling Krillin later right before the Cell Games that just being with her and his son is everything to him and all that really matters to him

~Chichi's devotion to him is very touching to watch. She never leaves his side when he was recovering in the hospital after his battle with Vegeta (she even knits him a sweater hehehe) and later when he's sick with the heart virus

~Then there's the point Goku decided to stay dead, and, well, marriage is generally 'till death do you part so she could have moved on and been well within her right to find happiness with someone else but she didn't. That was partly because she's a strong, independent woman and also out of sheer devotion and love for her Goku. And just look at her reaction when Gohan first tells her he's coming back for a day in the Buu saga. That's exactly the reaction I'd expect out of a well-loved woman hehehe