People still need to buy the cars. Just like Dieselgate has killed diesel, people will vote with their wallets if manufacturers start trying to pull the wool over customers' eyes.
Also obviously a 1bhp hybrid would get awful fuel economy figures compared to a real hybrid. If you are a manufacturer and you go to all that bother to build a hybrid, why bother doing a 1bhp motor instead of a 30bhp motor? Whats the point? Just to "get around" the law? Why not just put a proper motor in and make a better, more competitive product? I doubt the cost of a 1bhp motor is much less than a 30bhp in the grand scheme of things needed to build a hybrid car (e.g. batteries)