Increasingly better quality sires are playing a big part
Firstly, there's a reason why the Industry, as compared to years past, is able to conduct significantly more races per year than before with less than half the number of foals produced annually.
The introduction of open books combined with the adoption & use of semen transport has seen the influence of infinitely better quality sires spread far & wide.
This has in turn resulted in vastly improved starters to foals %'s...and also those that do make it to the track make more starts each season/lifetime than did their predecessors.
Today's Standardbred is a better gaited, better conformed, more athletic, precocious, faster, sounder and far more durable article than it has ever been before.
Southern Hemisphere experience will mirror that of the Northern Hemisphere.
We will similarly see continued compression of the times being posted by the best 2yos through to the best Open Class performers and that compression of times/records will be active at all points down the ladder.