First and primary reason: Low Quality.
Most debates are poorly done, involve low effort, and look boring. I think most of you just don't understand how to substantively engage in fact/reason based discourse. There are presumably many reasons for this, tangential to the observation I make here, but reading bad writing is to me like listening to music out of tune. I'm just not interested in it.
I think as well most of you just aren't very good writers. Obviously maybe you could improve a bit here if you wrote a bit more, but it is really hard for me to be invested enough in any of you to be willing to spend the time to teach you how to do something. Even if I did, I think there's an alarmingly high number of you who would resent my pointing out your lack of excellence.
Too many of you have the idea that judges should just praise debaters for their effort, which I think is stupid. Many of you struggle to form coherent sentences. Your writing is bad. Your arguments are contradictory. You do not know how to use evidence to support arguments. You do not know how to structure arguments in support of conclusions. You do not know how to even engage in thesis-driven writing.
I blame your lack of education. Teaching people to write clearly and effectively takes time and skill, which I am confident nearly all of your school teachers lack. I think in twelve years of public education, I had not more than three teachers who could write coherently themselves, and one who knew how to teach others to do it.
Despite this, if I pointed this out to you, would you not resent me for it? Do you not already resent me now for pointing out this fact? Of course you do, because when you hear criticism you don't take it as "this person cared enough to tell me how not to continue to be stupid." You interpret it as a personal attack, which you respond to inappropriately. So, why should I bother?
Second Reason: RFDs take too much time
I used to write long RFDs, and I had lots of reasons for that. I wrote the gold standard for what counts for a sufficient RFD, back on DDO. Some of you may still have that thread. Now, my time costs money, and the rare chance I have to do something leisurely I'm going to do something I enjoy. I do not enjoy writing RFDs for low quality debates.
If I could just give a three sentence RFD evaluating the major points and weighting them, I'd vote more. Surely most people couldn't and shouldn't do that, but that's all I have time to do. However, there are likely so called voting mods (lol) who would think that wasn't enough, and I'm not going to deal with that bullshit.
Third Reason: Debate topics are uninteresting
Most of you chose stupid topics for debates. Either you're biting off more than you can chew, the resolution is vague or unclear, or you've done some other weird shit that fucks it up for everyone -- debaters and judges alike. This is uninteresting to involve myself in. If you want my attention, pick a topic that's interesting.
Here are some interesting topics:
Alan Moore at DC was better than Marvel anything.
The United States should make substantial efforts to curb China's expansion in Africa.
China's ascendence places the United States at a geopolitical disadvantage.
Vladimir Putin has been bad for Russia.
Tarkovsky was a better film director than Kubrick.
Dostoevsky was a better author than Dickens.
Canada should substantially increase military expansion in the arctic.
More than anyone else, American media are to blame for Hillary Clinton's loss in 2016.
The United States should pull out of Syria.
Bashir Al Assad should remain in power in Syria.
Bibi Netanyahu's indictment is justified.
The United States has a moral obligation to support pro-democracy efforts in Hong Kong.
The list goes on...
I can think of dozens, but you get the point. Topics that have been beaten to death, where the political fault lines are so firmly cemented that no one is going to move on them, are not interesting. Figure out what you think, and then be gracious enough not to inflict it on the rest of us.
Fourth Reason: Nothing in it for me
This is the one you all should be focusing on. What does it benefit me to judge what you write? Am I more likely to be subject to your emotional reactions, or am I more likely to be thanked? Even if thanked, why should I bother? Really, sell me on it. Maybe there's something I'm missing here beyond the so called reward of simply "giving back" or whatever other bullshit you can come up with. If so, tell me why I'm wrong. But from where I'm standing, voting is electing to draw the short end of the stick while knowing that's what you're doing. No thank you.