The answer is in the question.

Making use of existing "capital" is "cheaper".

When I need new shoes, or a new keyboard+mouse, I will try and find the same model I had before, because I know it worked for me.

The last time I bought different shoes I ended up bleeding through my socks because they were not a good fit.

There's a possibility that they give me a defective version of the shoes I like when I buy it, but in my mind there's less risk of having an unsatisfactory result.

Sufficed to say, they are willing to take a smaller gain on what they believe is a sure thing than try something they believe is risky but has the potential to make great gains.

With few exceptions this is the way most parts of the movie industry are going. Some exceptions are the indies, the horrors, and the rare chances that blow up (Joker) and you can see the difference in budgeting with those projects.