Porsche's 1987 withdrawal from the WSC

Can anyone shed some light, if possible, on the reasons behind the withdrawal of the factory Porsche team from the World Sportscar Championship mid-way through the 1987 season? I know from season reviews that, after Le Mans and the Norisring sprint, the factory team simply pulled out and left Derek Bell and Hans Stuck, who were competing for the Drivers' title, high and dry until they were snapped up by Reinhold Joest for the rest of the season (except for Fuji).

I'm really curious as to why the team made this decision.

Can anyone shed some light, if possible, on the reasons behind the withdrawal of the factory Porsche team from the World Sportscar Championship mid-way through the 1987 season? I know from season reviews that, after Le Mans and the Norisring sprint, the factory team simply pulled out and left Derek Bell and Hans Stuck, who were competing for the Drivers' title, high and dry until they were snapped up by Reinhold Joest for the rest of the season (except for Fuji).

I'm really curious as to why the team made this decision.

I looked up the 1987 season review in Ian Briggs' book 'Endurance Racing 1982-1991', and to be honest it doesn't give a clear single reason either, though it says 'the reasons for retiring from the series were many and varied'

Briggs lines up a collection of circumstances that could have caused it, including the Porsche racing department being fairly stretched with Group C/IMSA, the TAG F1 engine for McLaren and the March-Porsche Indycar project all in progress, the relatively low media profile of Group C compared to F1 and CART making it the easiest to drop from a commercial angle, the possibility of freeing up resources to concentrate on a successor to the 956/962, which was getting fairly elderly by '87 (and the 956 of course outlawed by changes in the chassis regs for '87), plus FISA's regular meddling with the Group C regs and apparent lack of interest in the category (a set of proposals released in late '86 hadn't gone down well with the teams- I think they included the idea of dropping the fuel formula)

The conclusion the author reaches is 'So when Jaguar started dominating the early part of the 1987 season, it must have seemed a perfect time for Porsche to withdraw as gracefully as it could'

Something I'd definitely forgotten is that Porsche originally announced only a 'restricted programme', then changed that to a full-season 2-car squad by the time of Monza- then, as you said, pulling the plug on the programme after Norisring.

The development of the Indy-Porsche 2708 was in delay, and they did not much like the beatings from Jaguar.