Because people online are choosing beggars.
They think they can post up a list of every desired character trait in a partner, and that some magical person is going to come along and fulfill all those standards.
Also, IRL, we take people at face value, without the checklist.
We get to know them organically, gradually, to learn their positives and negatives.
On the internet it's like sales catalogue: photos next to stats. Very.... unromantic.
And then the instigation of conversation via text, trying to think of something witty, unboring, but not too strange - it's all very absurdly curated.
IRL you can absorb facial expressions, vocal inflections, tones, body language, etc.