Lack of regular maintenance, lack of appreciation and unsuitable storage often leads to their demise unfortunately. As Jean says, circumstances change.
Well you are probably too young to understand what went on years ago.
I bet that there is not one oldie here that can't look back and reflect 'if only I had kept my old cars'.
One of the biggest problems was in 1974 when we had the 'oil crisis' combined with a 3 day working week. Money was in short supply even with the better off. I was fortunate being in the Royal Navy I was fed and clothed on her majesties service and received full pay so managed to save up. At this time I saw an e-Type for sale. Prices had plummeted from the original £2600.00 new price and I bought mine for £690.00. I did have a lecture from my late father at the time who insisted I should invest and buy a house....but took no notice......being young. I still have the car today, yet back in 1987 another crisis (stock market crash) saw its value drop from some £100K way back down to £30K indeed as did my 246 Dino. Only today has the Jaguar caught up again. I made a huge mistake and traded the Dino for a 308 then saw over the years the Dino go up to prices around £350K and strangely the 308 has remained fairly static over the years despite being one of the last Weber carb models. The original fibreglass bodied ones though back then you could hardly giveaway and now fetch up to £250k.
Cars values seem to follow a J pattern over the years. They start off at a price then devalue till they reach the bottom of the curve. At this point repairs and parts cost are just not worth it with respect to their value and often no one wants to buy them. As the years progress and the numbers get less the values start to increase. Also secondhand parts become available and it is worth the restoration. (on some:devil). Gradually prices just start going up and up then.
I just don't understand the Shadows, maybe because there were more made and not so rare but many of the cars you pictured would well be worth restoration. I still doubt though the investment unless small is worth it today on a RR Shadow. Indeed strangely now the Bentley's which was always classed as the poorer (not poor but poorer) mans RR are fetching more money than the RR.
I can see you are still inbetween deciding what to do with yours.... but think to the future where all these cars may end up. It was only a few months ago two ladies were waving their handbags at me when I was in the supermarket car park telling me I had no respect for the climate in a gas guzzling RR car. Not withstanding they were pushing their shopping trolleys full of plastic bags. Also someone posted recently about converting a RR to LPG as Madrid had banned ALL petrol cars from the centre.
At my age I doubt I will be around driving cars much longer now and likely be on a forum no doubt with battery scooter problems or fixing punctures on wheel chairs.
Of course all over the world there are abandoned RR and Bentleys. For some ,the first owner passed away and the heirs haven't had the finance to maintain the vehicle. Other than these extreme cases, one may recognize that the the replacement parts are pricey. I am new to this forum but the first feeling that had is that the members are outstanding , they are always doing the best and the most for these masterpieces to stay on the road. I believe that for all of us, to contribute to having less and less RR and Bentleys in ruin we need to have access to reasonably priced parts. Of course price is not the critical factor for quality is crucial. I have a dream that sooner it will be less a hassle to get cross referenced parts, I have a dream that one day soon we have more shops to compete with flying Spares. And when all of us through out the world have access to parts without spending our nights and weekends scouting the Internet, then, each one of us would have bravely and happily contributed to reduce the number of abandoned RR and Bentleys.