I was wondering myself why people choose other engines and I came to the conclusion that most people choose Gamemaker because it has better performance since it exports to native code???
Modern JavaScript engines are exceptionally fast, and we've carefully tuned our engine for performance over several years. On my development system it can manage hundreds of thousands of on-screen sprites and still hit 30 FPS. I would think it is at least strongly competitive on performance. Who knows, maybe it's even faster? It would be interesting to see actual benchmarks. But I think Construct is fast enough for the vast majority of people who use it, and of those who have performance issues, often it's hardware limitations like GPU fillrate that won't be improved by changing software. So I'm sceptical many people would choose other software for performance reasons alone.