Will they be too busy to work on it? Will engineers like this be interested?
1) am I getting paid by the hour (or day or week)? Or does this employer expect me to be able to predict in advance how long this software will take to develop, and agree on a total price ahead of time? As a large company, perhaps I could overcharge for all jobs, and then the ones that do not go over budget compensate for the ones that do. As an individual, I cannot take that risk.
2) does the prospective client seem easy to work with? I don't have management, legal team, etc. to guarantee that the relationship doesn't turn nasty. If they seem jumpy or nervous or too hard-driving, then I am better off leaving them to a company, which has the legal and managerial staffing to deal with that.
3) I am a full-time freelancer; if I were currently working for FAANG, I probably would not want to do significant work on the side, unless it were for my own potential startup. FAANG developers probably already make enough money that they don't need to take side projects.
Hope that helps!