That one has 330mΩ max. for both high side and opposite low side in series (at VM = 5 V; VCC = 3 V), so well under the 500mΩ you claim is common.
MOSFET on resistance depends on channel geometry, gate oxide thickness and gate drive voltage. In general, physically larger MOSFETS, driven harder have lower on resistance. However that costs more silicon die area and may be incompatible with the low threshold voltage (typ. less than Vlogic/2) requirement for direct logic drive. Also it does't take much power to run a cellphone vibrator motor so low on resistance isn't a priority in the main market for low voltage motor drivers.