I don't this anything happened 'suddenly', perhaps some people only noticed it at a certain point, when it became impossible NOT to notice that laws, medicine, education, language, etc., were all being altered to cater for a very small number of people in society, in a way which had never been done for, for instance, disabled people.
So for some people, there was a sudden WTF is happening moment.
But many of us noticed things happening more slowly: the term 'transgender' replacing 'transsexual'; the rewriting of lesbian and gay history; the replacement of the word 'sex' by the word 'gender'; the unsolicited appearance of the T in LGBT; the unsolicited downplaying of the L in LGBT; the suspension of standards of medical ethics in certain areas; etc.
It's a pity the calm rational voices speaking scientific realities years were not listened to back then.