Why is there a difference in LP when we win vs lose?

LP gains/losses depend on your mmr relative to your rank. If you're silver 3 ranked with a gold 3 mmr for example, you'll be playing with/against gold 3s, but you'd be gaining like 30 LP for wins and losing like 10, since the system is trying to ensure you climb so your rank matches your skill level. Conversely if you're silver 3 but have a bronze 3 mmr, you'd be playing with/against bronze 3 ish players, so progress will be slow since LP gains would be smaller than the losses.

The goal is to get you to your skill level ASAP (i.e. correct mmr), where you win ~50% of your games. Then by tieing LP gains/losses to mmr, that 50% winrate will still result in people climbing/falling as appropriate so eventually their rank will match their mmr.

I sometimes gain 25 lp but only have ever lost up to 18 I think it depends on your mmr