The routing options offered on the main page are there to show that OSM data can be used for routing. I very much doubt that this facility will ever be extended to offer: a) alternative routes; b) via points; and c) route dragging.

The reasons are that the routing engines which provide the routes are all third-parties who also offer fully featured routing options as a business. Their co-operation is predicated on the synergies between getting a larger number of people exposed to their routing engine; more eyes improving routing data etc.

Additionally, the development & administration of the main OSM website is undertaken by volunteers in their spare time: additional routing features would likely require a lot of development and could overextend devops.