The “tier 3” in that page is only meant to reflect the current status of the port. When it starts booting to the desktop it will be tier 2, and when there is an haikuports builder, and we ship an official release for it, it will be tier 1.
Developers gain experience in porting software to new platforms.
Haiku gains some “advertising”, as surely “Haiku gets a Motorola 68000 port, a CPU that has not been updated for 25 years, before the OS even started to exist” makes a good news story. And, who knows, maybe a few more users installing it?