Why open source is better

With an ever shifting geo-political landscape it's more important than ever that your critical business functions can continue uninterrupted without outside interference.
With open source software you can own a copy of the code that's driving your marketing pipeline or providing per-user personalisation of your e-commerce checkout. The data lives where you want it to too, helping you to comply with legal and regulatory requirements.

With closed source software you're at the mercy of a third party, they could pull the rug out from underneath your business at any moment. Or if they are based in a foreign country they could be compelled to stop providing their services at any moment.

With open source software you can see the code and exactly what it's doing. There's nowhere to hide. Your internal security teams can view the code and see exactly what the software might be up to.

Closed source software is a potential vector for supply chain attacks where some malicious actor at the third party vendor includes some code that scoops up your API credentials and sends them off to be used against you.

Security researchers can read through the source code of open source software, like Drupal, and find and responsibly report issues and then everyone benefits from that improved security. With closed source software who knows if white-hat researchers will find the issues before attackers and even then you don't know that reported issues are being fixed rather than being swept under the carpet.

Drupal allows endless customisation so that you can tailor solutions to fix your exact use-cases. You can tweak the entire application making it do exactly what you want.

If you need a feature developed then you're not beholden to some third-parties' development roadmap, desperately hoping that they are going to add that feature in version 2.0.

If Drupal needs to integrate with some third party system and there's not already an integration for it, then you can use either your own in-house developers or one of the thousands of developers around the world to write the code.