Those are really high split rates. We (as in UFB in NZ) looked at 32:1 splits but it's rare - in practice it's often half that. Splits end up based on contention of regulated L2 plans which are sold to RSP's to on-sell to customers. Based on available backhaul bandwidth rather than any factor. i.e on a 2.5Gbit Duplex GPON port which carries a L2 service to RSP(L3 providers) it's a simple matter of dividing up the Active Optical backhaul to the GPON unit (minimally 2x10Gbit Active Paths to the CO for an old style GPON only node) so that gives you around 66 customers on a 300/300 service without resorting to Teletraffic engineering in the access equipment. Splits per line card port are then distributed based on that metric rather than anything else. There are of course some exceptions to this rule for some nodes in the network but it's uncommon.
RSP's are responsible once the L2 is handed to them, so experience varies once it's off the access network. But the entire PON network is engineered without contention at any points, including in the last-mile, it actually works out cheaper than introducing engineering required for massive contention ratios and results in better experience for everyone.
The active GPON nodes used in the network mostly have been moved to 2 or 4 * 40gbit or 100Gbit uplinks at the this point to support XPON.