Persistent MIDI note length errors

Just did a MIDI loopback test*, before and after installing the update…

BEFORE update
-note start errors up to 10 ticks
-note length errors up to 4 ticks

AFTER update
-mix of perfect timing and note start errors of only 1 tick
-note length errors up to 4 ticks

Why do the MIDI note length errors persist?

With the amazing speed and power of modern computers, which can handle audio data with microsecond accuracy, WHY ARE THERE ANY MIDI ERRORS AT ALL?

*16th notes at 120bpm, as advised by SteveInChicago in this post…