Anyone know the rationale behind the stricter definition of a relevant family member, for fee purposes?

[kamoe]

If you are in the UK as a family member of an EU citizen and want to pursue higher education studies, you might or might not qualify for EU/Home fees. It all depends on two things:

1. How long you have been in the UK (minimum 3 years)
2. Whether you are a 'relevant' family member, which pretty much excludes unmarried couples.

While I understand the reason for No. 1., I just don't know how No. 2. makes senses. If you are an unmarried partner and have obtained the status of residence in the UK on the basis of your unmarried relationship, why on earth would there be a restriction on the fees you need to pay? Anyone know an official, written rationale that's available for reference?

Thanks.