Although people often compare LXDE and the “so-called” Qt port, LXQt with each other, they are actually from different code bases.
The most parts of LXQt are actually built on top of razor-qt, a lightweight Qt-based DE with the same philosophy as LXDE. We reorganized the source code of razor-qt and removed unused pieces. Then we ported several LXDE components to Qt and also developed some new ones. Hence it’s more the merge of developers than the merge of the actual source code. That’s why they have slightly different feature sets.