Probally sounds dumb but i think its becaust its a even number. KInda like when we celebrated the bicentenial of america in 1976. Sure every year were still america, it just signifying that its been 200 years. And at some point there going to have a 250 year america celebration. Its just because its a flat number of 300 is why its a celebrating point. Kinda like when we make big deals about or 30th or 40th birthday. There milestones so speak, Because theres a 0 after the number it makes it that much more noteworthy. Most people might not be around for 500. And the record might stop one day so kinda celebrate it while its here.
Does that help.
Ben