The headline is wrong, there is nothing about banning motorcycles or motor-homes from entering Thailand in the article. In fact it is actually about slowing the numbers of cars from China, reporting bad drivers, and charging for road use.

The reasons are clear to me, that most Chinese car drivers are only used to driving on the right, have a very self-entitled attitude, and also don't understand or ignore the whole concept of yielding/right of way and major/minor roads. Not every driver is bad, but a majority are, and, with every country the worse the driver, the better they think they are.

Also Chinese drivers are free to drive into Thailand but it's impossible for Thais or anyone else to drive into China. There's only so long you can have your cake and eat it before someone calls a halt.