Usually it is because the startup folks do not have the experience to even know about Oracle servers. And there is a strong tendency for younger people to choos

Usually it is because the startup folks do not have the experience to even know about Oracle servers. And there is a strong tendency for younger people to choose technology by imitation, in other words use what your friends and acquaintances use. From a business viewpoint, making a tech decision that way is better than picking at random, but even better is having someone with grey hair around who can weigh the pros and cons of different tools and match them up better to what the startup is doing.