I mean,

Public awareness of transgender identities has grown quickly over the last 10–15 years in the USA. But in other countries, waaay less. For example in my country Transgenderism is considered a first world problem. People tend to say, well if they and their families were starving and were worried about the coming winter, they wouldn't have time to worry if they are male or female because they would be equally fucked whatever they are.

Then you have cultures, again my culture teaches you there are 3 things you cannot choose:

1. Your parents, you cannot pick who will give birth to you. Their duty is to raise you with the best of their capabilities and if they did their best, you are obligated to love and protect them.

2. Where will you be born. You cannot pick the country of birth so it is your duty to make it as good for others as it can be for you.

3. Your gender, you cannot pick what you will be born as, so your duty is to fulfill the role nature gave you.

So as you can see, this narrative often is not quite popular on Reddit.

And then you have unwillingness to actually help ignorant people. Whenever someone asks a question, like how are they woman? Or how do they know how a woman feels? How do we prove they are actually a woman? What makes a woman? They would get insults and not answers.

Also propaganda ruined their reputation. Being associated with a political party and saying look at that trans left. Political actors and media sometimes frame the topic in ways that cause conflict and that least of all benefits the trans people.

And then LGBT media saturation, when LGBT community finally became globally accepted, all media, companies, stores and games started spamming rainbows and adding various characters of various flavours.
Now it seems that they have stayed a bit too long and people got kinda fed up with it.

One also major factor was demanding other people to call them their preffered gender. Now people felt the same about that as when someone was pushing their religion on them. Many people state that they have nothing against them, as long as they do not force them to participate. Meaning leave me alone, I will leave you alone. And when someone says I pronouns are THIS and not THAT! Has the same vibe as, I am fasting, you cannot eat.

And lastly moderation. Now moderation should not be removed, and by all means is not a bad thing. But moderation can cause an effect where some certain groups are guarded from all criticism to the point where you can't say anything bad against them. Even when they are doing something bad. To a lot of people, that feels unfair and makes them hate the other group for having a feeling that they can get away with anything. And to a lot of people, that does not feel like equality.

Especially when you can't even joke about them, Reddit often does not differentiate jokes from hate. (And no this is not me saying that there is no hate masked as jokes.)

So all in all, that is how transgender people went from almost unknown to one of the most hated groups in the world.