Interesting. Could you explain why this is so?
I dunno, but will throw some thoughts out there...
with negative offset, when you step on the brakes, the tires pull trying to steer outward causing extra loading on the steering(and all the rubber bushings holding everything against it). Bumpsteer will increase. A flat tire will pull hard enough it will be tough to keep it straight.
as much as I always hated the look of 'flat faced' or front wheel drive looking wheels, they are best for a lot of reasons...if theres enough positive offset to put the tire centerline on the balljoint centerline, scrub radius becomes zero- so on a car with FWD or ABS brakes, steering pull will be eliminated, a flat tire wont try to spin the steering wheel out of your hands- neither will hydroplaning one tire if theres water along side of the roadway. Moment loading of balljoints/control arm bushings/wheel bearings will be as low as possible, resulting in the least deflection under cornering/braking loads, etc, etc, etc...
I still like the look of deepdish wheels though. the deep18x9's I got for my 06 mustang, they actually curve the spokes out to allow appearance of the deep lip, still with a positive offset...dont look as good as the old ones, but not a bad compromise. too bad noones making longer A-arms and offset wheels for these old cars, theres a lot of room for improvement at minimizing scrub radius, if a nice deep lip wheel(even the new mustang deepdish wheels) could be fitted also, could have the best handling possible and still look kinda traditional...maybe someday.