I was thinking about this problem and while I get your point that using old technologies is limiting the people you can bring to the project as new hires may not know them or not willing to use them, I also think that you miss a key point here. The most expensive part of a software project is it's maintenance. A monolyth is easier to maintain and you need less DevOps engineers as you will be maintaining a single architecture. If you have multiple teams maintaining different platforms, each written in it's own language you will need more people to support that as well.
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I was thinking about this problem and while I get your point that using old technologies is limiting the people you can bring to the project as new hires may not know them or not willing to use them, I also think that you miss a key point here. The most expensive part of a software project is it's maintenance. A monolyth is easier to maintain and you need less DevOps engineers as you will be maintaining a single architecture. If you have multiple teams maintaining different platforms, each written in it's own language you will need more people to support that as well.