Hello I'm completely new here and wanted to ask if there is a reason why the old Elder Scrolls Games (before Morrowind) aren't on GOG. Thank you in advance :)

For the same reason Morrowind and those after are not here either. Bethesda has not joined the party yet.

Hello! They aren't on GOG because Bethesda is not signed up to distribute their games on GOG. Hopefully one day!

But as for the games, they are freeware and you can get a GOG-like installation package from these two sites. Hopefully that will help you out.

[url=http://theelderscrolls.wiwiland.net/?title=Arena_:_ArenaSetup_EN]http://theelderscrolls.wiwiland.net/?title=Arena_:_ArenaSetup_EN[/url]
[url=http://theelderscrolls.wiwiland.net/?title=Daggerfall_:_DaggerfallSetup_EN]http://theelderscrolls.wiwiland.net/?title=Daggerfall_:_DaggerfallSetup_EN[/url]

EDIT I linked the French version of Arena for some bizarre reason. Fixed.

Oh thank you very much for the links and the answers guys!!! :)))

Daggerfall and Arena are freeware now, you can grab it from Bethesda's website. They are a bit annoying to install. There's also a fan-made window installer version, it is easy to use and includes some patch and tool. However, it is NOT the version Bethesda releases as freeware, so the contents might have minor differences.
PeanutBrittle has posted that version

It's nice that the newer people have begun protecting these questions. It's a bit like in the school grounds when the year above you run over an says "don't play there, they'll hurt you over there".

Good job guys, the wheel is going round.