Hello.

Got an .ai from the web and after working on it a bit I tried saving it to .png and voila, text doesn't show up, don't know why.

Please take a look.

Do File > Export PNG image and make sure you have selected the 'Page' tab in the dialog, not the 'Selection' tab.

Perfectly worked, but why?

The question is: what did you do differently?
Did you Save as... > Cairo PNG? If so, then the explanation is that Cairo PNG is not the same as PNG - it has a limited feature set, e.g. it doesn't support transparency and some other features.
If you had selected a different export area, then that's the reason.

I guess the confusion comes from this:

in AI (and PS) you universally 'save as...' (.ai, .psd, .jpg, .png, etc.).

While in Inkscape (and Gimp) you 'save' a project (svg, xcf), but Export as .png (also .jpg and other imagetypes in Gimp etc.)

Yes, I was saving as Cairo PNG, didn't know it's different.

Thanks.

You're welcome!