This is more of a design decision question..
I see that if you have a field value of type DateTime it will be saved to Influx as a number (Epoch). Obviously because Influx does not support DateTime data objects.

But if I read these measurements back, there is no way for this library to convert it back to a DateTime.

So what's the reasoning behind the decision to convert it to a number/Epoch?

It seams a bit useless and perhaps wrong IMHO.
Perhaps the user should do the conversion himself instead of the library making this decision. Then we can decide to use Epoch, another number, or perhaps a string... At least then you have the knowledge to convert it back to the original type.