DisplayPort daisy chain is specifically unsupported by Mac OS since forever. If you dual-boot an Intel Mac to Windows (via BootCamp) it'll daisy chain just fine, so the hardware supports it, but booted to Mac it'll just ignore the second monitor in the chain.

If you are lucky enough to own a Thunderbolt (note: not displayport) monitor, that can chain to a displayport monitor. But thunderbolt monitors are rare as all get out these days.