PostgreSQL is open source, and then, there are several companies that could give you technical support, like EnterpriseDB or Percona.
PostgreSQL is easy to install and configure and is multi-platform, you could use Windows, Mac, Linux, FreeBSD, and you could use ALL the hardware you have purchased for your project, without sinking hundreds of thousand of dollars in proprietary software, to use only a small part of your server for the database.
Let's see a concrete case: You have a project to make an information system which uses an underlying database. Then you purchase 3 servers, which cost USD 50K for the Production server, USD 25K for the Contingency Server and USD 10K for the Development Server.
If you use a proprietary database, we know what companies, they price their software licenses per every 2 cores if we use the servers physically or every 2 vcpus (threads) if we use virtual machines, and the cost range is between USD 15K and 50K for each 2 cores license. If my production server has a configuration of 24 SSDs of 3,84 TB, 2 TB of ECC RAM, and 2 CPUs AMD EPYC 7702, with 64 cores each (128 cores and 256 vcpus or threads per server), the cost of the proprietary database could be more than USD one million, and if we use a subscription mechanism to get the updates, we could be talking of another million each 3 to 5 years. That is ten times the cost of the hardware. And you can TOUCH the hardware.
Is PostgreSQL slower than the proprietary databases that we talk about? Yes; but for what margin? In in-house tests, the performance of PostgreSQL was from 50% to 75% typically, with several scenarios where PostgreSQL where speedier. But we could use ALL the cores for the DBMS, not just a few.
For us PostgreSQL is the best database in existence. Period. If we use proprietary databases yet it's only for legacy information systems, for contractual restrictions or because our providers haven't seen the light (yet).