Well your other choice is you pay for a non open source SIEM that's $10 per endpoint per month and cross your fingers that they don't do a rugpull and start charging you $20 after it's insinuated itself into your environment is hard to replace..

With an Open Source project you at least have the possibility that if it has enough users and companies using it then someone will fork the code if the company ever makes it closed source and keep the project going.