A guild that expects loyalty, also has a responsibility towards its members, to provide the challenge and environment they seek. A guild that says "yeah, we are a progressing raid guild, but we stop raiding for the next few months, because reasons", cannot expect members who want to raid and progress to remain loyal. Its a contract that goes both ways.
Most guild leaders, and in fact most people forget that part. No, a guild is not entitled to have and retain members, it has to work for it, just as members have to work for their spots.
If your guild expects you to stay and remain loyal, despite not providing you with what you seek in a guild (in your case that's progressive rading), then you are fully within your rights to seek out greener pastures.
If that creates bad blood, well, then you know that the GL doesn't understand basic facts about guild-leading.