Runway 28 needs the steep approach to clear the East London River Crossing, to the east of the runway and just where the flightpath crosses the Thames. Now this bridge has not been built yet, despite having been planned since long before LCY opened 20 years ago, and is subject to constant yes-no decisions by politicians, but the steep approach is to clear its location if/when it is built. One of the original planning conditions on the airport when first built was it should not compromise this planned bridge.
The bridge will be quite high to allow seagoing ships (still quite a few come up the Thames ths far) to get underneath. For example the sugar refinery to the immediate south of LCY has ocean-going freighters delivering raw sugar cane from the Caribbean. However unlike the bridge on the M25 at Dartford it will not have piers above the bridge deck. If you look to the north as you cross the river approaching 28 (when pax-ing only of course !) you will see some initial signs of construction of approach roads, which have laid unused for many years.