>>17278615The explanation in the show was a decade of trail and error. The only planet they could dial was Abidos because they were not taking into account stellar drift. They weren't able to actually interface with the software running the gates until they met the Asgard.
Image you have a telephone that had it's own switch and exchange via the DHD. Here the switches and exchanges are updated by the phone company whenever a new person is added. Now imagine if your own phone was just hard wired to the phone network, but was only programmed to dial numbers form, say, 20 years ago. Most of them will not longer work because of customer changed (steller drift) Abidos' address has just has just never changed.