The usual problem is that the various cross-platform UI toolkits not only fall into the uncanny valley but also only support one programming language best (in this case, Pascal). Only the incentives of the biggest cross-platform browser vendors align in such a way that they pursue native UI effectively.

Recent discussion: Why I use Object Pascal | https://news.ycombinator.com/item?id=15490345 (2017Oct:268points,233comments)