1. Crash reports only report crashes. We need also want to see perf issues like GC and paint jank, etc.
2. Crash reports don't sample the general population, so statistically the information is less useful. If we get a perf issue, it's very important to know whether that issue is suffered by 10% of the users in general pop, or 0.5% of users in general pop. You want to prioritize the stuff that has the greatest impact on the general user population.
Lastly, crash reports are sort of a boolean filter - you only get the people that crash. The things I'd like to know to help in my development are things like "what is the histogram of max GC pause times on docs.google.com". Getting that info requires a good random sampling of the population, not just those who exhibit problems.