I reckon people give up because:
Hassle factor
If you rent from a club you get loads of hassle.
Examples that have happened to me include: You book a 2 hr slot and the aeroplane comes back late and needs to be refueled. The transponder has been removed and put into another aeroplane as they are using it for instruction. The plane you booked has got tits so you're shoved in a grotty replacement. The VOR has stopped working. You need to fly 3 hrs per day. etc....
Cost
For the privilege of the above you are charged £130+ per hour plus a £30 landing fee
Boredom
During your 2 hr slot you are limited to certain airfields. So you fly into the same one again for that expensive burger. And you know the route well so you are relaxed, but it does get boring. You cannot train for further ratings due to the ALL or NOTHING approach of UK flight training. You thought about starting on the IR but a) you have to work for a living and b) suddenly the costs jump by £50 per hour for the instructor to train you. The result is you don't bother.
The only way to address the first two points are to get your own share. I bought a share and it is the best thing ever - my aeroplane is not particularly expensive to buy / own / operate, and there is NO hassle factor. I just turn up, wheel it out of the hangar and off I go...stopping over night if I want. Costs are minimal and fuel burn is only about 31 litres per hour.
For the last one, well having a share helps, with not being limited to daily minimums. I also head off to the USA several times a year for a completely different type of flying. Whereas in the UK my flying is mostly SE VFR due to aeroplane and equipment limitations, last night I had a great IFR flight in California in a DA42 with 100hrs on the clock and all the bells and whistles - (Nexrad, XM, traffic etc...) at night, 1000'OC with frontal weather, hand flying in moderate turbulence, rain so hard it was like a freight train hammering on the cockpit and it was FUN and cost me no more than a crappy PA28 in the UK.
There is a place in California which now rents brand new DA40's (Avgas) with G1000 / traffic / XM etc (possibly with Synthetic Vision - amazing piece of kit) for $99 per hour DRY. With careful flying and lots of airports the fuel can be kept to under $40 per hour - so for $140 per hour you get a mean machine with all the mod cons and get to see some interesting places. Anyone who is bored of flying in the UK should really consider a flying holiday in the USA.