I think it would be a lot of work for Jagex to do that, since it would mean rewriting some quests for those races. For example, if we started out as an elf...
Would we begin in Lumbridge/Taverly, or the elf lands? Wouldn't we already know we're being deceived by King Lathas/Lord Iorwerth?
How different would tree gnome stronghold be if we began as a gnome? We wouldn't be seen as an arrogant human, and King Narnode (I believe?) might take us more seriously in our accusations that Glough is poisoning the tree
Apart from larger lore things (and probably even larger ones I didn't think of quickly), there would be a lot of subtle correcting, too