Hydraulic filters are expensive. They're much larger than engine oil filters and often have higher spec filter material. And the market for them is smaller.
Just because a filter has the same external size and threads doens't mean that the filter material is the same quality. Or that the relief is the same pressure, or that it
has or doesn't have the same anti drainback as the OEM filter. It's often impossible to get those values for both OEM and aftermarket filters to allow a true comparison.
Certainly when in warranty I use the OEM filters. For most filters on most vehicles I use OEM after warranty too. It's like using good oil.
HST and hydraulic innards on a tractor can be expensive to replace.