@Magisch I suspect the real reason is exactly that. Lack of staff, lack of decent designers. There's a shortage of personnel, a number of employees have recently left, which means the number of black diamonds is shrinking. Designing a site from scratch is time-consuming and costs a fair bit, and they need every hand on deck to finish the newish left-nav responsive thingy.
All of SE's energy and money is in developing that platform, making custom questions feature foolproof (can't be easy) making all that work, and making it look attractive for investors. Yep.... my money is on that. SE Writing will have to wait some more.