I believe they are so A**l because of how central it is to London. The approach to LCY is not the standard 3 degree..I think it is 7degree, hence you feel like you are suka diving the runway.
If your single engine spamcan went quiet upfront it could all go terribly wrong, and with Canary Wharf housing some of Europes major communications hubs It would not be a clever idea to allow such a risk.
At least with multi engine you have some sort of chance of staying straight and level or some form of powered approach.
As for helicopters I cannot explain this, maybe there is a lot of windsheer due to the builings around the airport.