(my experience as an expat with expat friends. Generally talking about residents of singapore, not necessarily born and raised here)

Food's not an issue. All the expats I know love hawker food, we just don't eat it very often because its mostly unhealthy. Some people don't care about their health, but most people do.

The language barrier is a minor issue. Even if you're not using singlish, the accent is generally pretty heavy. But its not inconvenient enough to block a friendship.

Singaporean's definitely don't come across as stiff or closed-off or unwelcoming.

The main thing for me personally, is we have very little in common. Most of the young people i've met here are hardworking, post-uni types who spend their free time going to networking/education events, or are heavily religious, or have started families at a young age, or many don't drink, etc. I have almost no common interests with the people I've met like this, and the few common interests we have aren't enough to sustain more than 10 minutes of conversation. I don't dislike them or anything, it's just a different lifestyle that I'm not interested in.

There are exceptions of course, and I've made a few local friends with enough common interests. I just haven't found enough to form a real group (I'm not particularly outgoing around strangers, so thats my fault).