Most of the time within a startup you can see developers stay in the company for ~1 year. Usually they are more willing to find another job than negotiating a salary bump ( which happens to be also mentally easier, since the first action is passive - just reply to a recruiter ).
When I completely switched to freelance gigs, I discovered that I stay in a company for far longer time. It is easier for me to index my price per hour with the market, since I have less bureaucracy with my client ( removes FOMO ). I had the best offers ( company shares + bonuses ) to join various companies than being an employee ( because of the FOMO of the employer that you might leave soon ). And finally I improved my code quality, since you always write your code with having your mind that sooner or later you will be not the code-owner.
Of course having 3 months off to enjoy the summer also makes it more appealing than the 22 vacation days you usually receive ( in Europe ).
Disclaimer - all of this won't work if you are a junior developer. Usually the stronger hands are in your employer then, since your contract can be terminated any day, without any notice.
But hiring a senior developer as a freelancer in your team ( IMHO ) will definitely mean that you will work with a highly motivated person, being there to do the job.