Because very often it's not up to the developer/architect to pick the technology to work with. Also what seems expensive to you, very often is not so for the customer.
At the place I work SQL with CALS and software assurance runs 300k. In a free market, I expect that soon people will build solutions on open source alternatives and undercut the competition dramatically.
Sure. But open source business models are not trivial to succeed or scale. RethinkDB is shutting down and MySQL ended up in Oracle's hands. Postgres is a bit unique, but still lacks good and friendly developer and management tools and better support from cloud providers.
As a counterpoint, we have a 2008 R2 instance that cost us about $13K back in 2011. Granted, it's a two processor, standard edition license, so we recently upgraded to SSD's and upgraded to higher core processors. Also, the Windows Server license was about $800, I believe. No CALs required for either Windows or SQL Server in this situation.
>No CALs required for either Windows or SQL Server in this situation.
Either you have Enterprise Windows (costs about as much as professional with the CALS), or the software you are running is only local to that server. The Microsoft treadmill is expensive.
> There's a special web licence for website, which doesn't use CALS.
Special licenses for various uses cases is another big plus for FOSS/PostgreSQL. Life is easier when adding database nodes or spinning up a dev/qa database is purely a technical issue.
"Windows Server 2012 R2 configured to run Web Workloads do not require CALs or External Connectors. Web workloads, also referred to as an internet web solution, are publically accessible (e.g. accessible outside of the firewall) and consist only of web pages, web sites, web applications, web services, and/or POP3 mail serving. Access to content, information, and/or applications within the internet web solution must be publically accessible. In other words, they cannot be restricted to you or your affiliate’s employees. "