It has been a long time since I've thought about it, so I might be misremembering, but the crystal geometry can influence skew related to orientation and external vibration. A crystal + IC design is using the crystal as more of a bandpass filter than an actual signal source, so it would make no sense to introduce the downsides of a tuning fork for a design that makes no use of the actual tuning fork quality.
It has been a long time since I've thought about it, so I might be misremembering, but the crystal geometry can influence skew related to orientation and external vibration. A crystal + IC design is using the crystal as more of a bandpass filter than an actual signal source, so it would make no sense to introduce the downsides of a tuning fork for a design that makes no use of the actual tuning fork quality.