Some of this might be difficult to set up but I don't think that's the reason why people don't use more pretrained models. If you have a working ML environment adding a pretrained model to it is trivial most of the time.
And even once the initial set up is done, ML software is constantly changing/breaking. You're forced to reinstall a new proprietary Nvidia driver, which is then incompatible with the old version of PyTorch the model uses... But that other model requires a newer PyTorch... It's a pain... The fact that there's a dependency on GPU driver versions is ridiculous.