This happens when personal interests get in to the budget. The 8 year rule was Mwiraria trying to help his son's business. He refused to go lower to help New Car peddlers. It looks like Rotich has given in to the same companies that Mwiraria resisted.
Some proposals are plain sick and beyond logic. Right now most countries are doing everything within their powers to stop people smoking. Thus anything that reduces the consumption of cigarettes and causes less harm is welcome. Son why is it now more expensive to drop a cigarette in Kenya?
Tanzania long ago allowed people who buy vehicles for business (Commercial is limiting) to escape heavy taxes. At some point it was duty free. Go and see how well that has worked. They have a clean fleet and the owners got lifted out of poverty. It happened at a time when Gideon Moi could import hundreds of new trucks, pay no duty and still influence the budget to make it harder for competition to import used vehicles.
About the 8 year rule: I think the whole idea of dumping as a reason for denial of entry is wrong. However now that he has opted to make money from old cars, should he not then lift the 8 year rule so he can make more money from the poor?