This is a recent development, and largely in response to homosexual ephebophilia amongst the clergy. The Abuse Crisis is undeniably homosexual, despite the fact that the age of the victims has been seized on more.
Therefore, this is arguably a recent and administrative rule, for very pragmatic reasons.
Contrary to your suggestion, I don’t think that changing this rule would matter to homosexual activists. I’ve NEVER heard it cited in connection with the Church’s alleged ‘intolerance’ concerning homosexuals, and frankly I don’t think activists and noise-makers in the anti-Church camp know or care.
OTOH, the LGBT reaction to the Courage apostolate and their mission of chastity makes PERFECT sense.
The LGBT community depends on an overt sexual orientation for a group identity. Chastity is the virtue of a disciplined and purified body. Embracing chastity as a personal or cultural value would deprive them of their overt sexuality or shift the focus away from it, and there reason for existence has been removed. And voila–no more LGBT voice in the intellectual/political forum.
Chastity is the only instrument available to silence the LGBT lobby, with charity, and achieve true ‘sexual equality.’