In no particular order as to why I left Reddit to join Lemmy:

• Reddit became a chore just to see good content. (This is even after the fact of filtering out unrelated or unwanted subreddits in my feed.)
• The comment sections on Reddit became worse and worse with more joke/meme comments than actually related comments, low effort comments, bot spam, and the burial of your comment for no one to see, (or care to reply to,) if you were to comment on a post or comment more than 24 hours after it's original posting. (Most of the time it felt like you had maybe 8 hours before it seemed to be a waste to comment.) Why would anyone stick around to comment or reply if nearly no one is going to engage?
• (Like many others have mentioned in the comments,) if you mentioned or talked about anything that wasn't considered good, you were often blasted with downvotes and/or comments.
• How often you saw rinse and repeat content, questions, and sometimes comments. (I'll admit. I took part in the rinse and repeat content 'sharing' and I wish I hadn't done it for so long. The karma whoring was real for me.)
• Concerns (then later the reality check,) about how much Reddit is an echo chamber.
• /u/Spez showing us who he really is.
• Not liking the direction Reddit was heading. Writing on the wall when they fired Victoria Taylor
• The API fiasco.
• Movement towards IPO.

Lemmy doesn't have any of these problems that I've experienced. Lemmy feels very much like a grass roots movement and I like that. I wish the communities that I am a part of had more active users, but that will more likely come with time.