My guess on the closing of the IOM route is that, since it started, both STN and LCY have had routes opened. Also, many routes from IOM to places like MAN and LPL have started that allow pax to link to European and other tourist routes.
There is an absolute finite capacity of traffic to/fro IOM and all starters have found that you cannot expand the traffic. When it was Manx that was running almost all the routes, then they could gain economies of scale. Unfortunately, BA wanted another four pairs of EGLL slots and bought the company. Then it was only a matter of time before they shucked off the rest. (and that's the polite way of spelling it.
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Aer Arran made a good start at picking up the LTN traffic but I think that the traffic had already been dispersed to the new routes. Looking at IOM web site destinations (ignoring Ireland North and South) there are 12 other destinations in England and Scotland, as well as LTN. When the LTN~IOM route opened I doubt that there were half that. (I sit to be corrected)
Incidentally, this is all my own view from using the route since it opened and observing the IOM as a regular visitor. I have no stats to back up my hunches, so criticise and put up facts as ye may! For myself, I am very cross that the route is closing as I have used it up to four times a year since it started.