When I win I gain 6 points. When my opponent wins they gain 29 points. Why?

Their rating might be provisional, meaning that there is a lot of uncertainty in their rating. This could either be because they are a new player or they did not play in a long time. Lichess' rating system has an uncertainty variable that results in wins/losses giving or losing more rating points if it is less sure about the player's rating.

Ratings only care about the result of the game. Ratings don't care about how the game was won or lost.

The higher the rating deviation, the less certain LiChess is about a rating, and the more it will change (both up and down).

Yours is very low because you've played a lot of recent rated blitz games.

Other people's are much higher than yours.

Looking at the first opponent's activity feed, we see that they had not played any Blitz games this year until today, putting a fair amount of uncertainty in their rating.

Looking at the second opponent's activity feed, they seem to have joined Lichess earlier this month and not have played any Blitz games until today.

In both cases, they might have lost the ? but Lichess may have still had a fair amount of uncertainty.

even if their rating isnt provisional their rating deviation could be high so they would earn lots of points still. they might have a rating devaition of 90 but it would be less than 110, so it wouldnt be considered provisional but they would still have their rating fluctuate a lot

LOL