Why is it impossible to upload saved Garmin tracks?

I tried to upload a saved track from my garmin handheld unit, and I am getting a report after track is processed:

loaded successfully with 2 out of a possible 502 points.

Of the failed points, 500 lacked

This means it is not possible to upload GPX tracks without time tag. Why?

I believe time tags are required for giving some evidence on that they are real collected tracks and not some possibly copyrighted vector data converted into gpx format. It is not hard to add artificial time tags into a gpx file with for example one second increments and make the file uploadable but even then by analysing the data it would be possible to see that they are not real field collected data.
If you have a Garmin unit like Etrex you should use the active log, read it with Mapsource and save as gpx. That way the time tags are remaining. Also configuring GPS to save tracks automatically into SD card keeps the timestamps.