I used to be like this. For me it was because I'm kind, proactive and lacked knowledge of how to deal with toxic people.
I don't want to know someone is suffering and stand by just watching, if I could help then I would. I'd met awful people before of course, but I wasn't aware of the type of person who smiles and appears nice on the surface but who, underneath that, is all take take take. I had some friends like that, so it was normal for me to be tolerating it. I didn't recognise it in my boyfriends or for a long time in those friends. My kind nature attracted "user" types.
I don't often share my problems, I don't believe in wallowing in things. I get on with sorting things out, somehow or other. I'd only say something briefly and downplay it. So if I'm sharing a worry with someone, having a big conversation about it, it's because it's serious and I can't think of a way forward. I had no idea just how lazy some people are. People can have good jobs, be ambitious, be passionate about hobbies etc and yet be so so lazy with themselves. I've come to realise there's an awful lot of people who don't try to fix their own problems, their go-to thing is to either lean on someone else constantly and forever whilst nothing changes or look to someone else to fix it for them. So I ended up investing heavily in helping others, thinking they must be having a really hard time to need all this help, when all it was is they were being lazy and taking the easy option.
The other problem was, having been in an abusive relationship in my teens, I'd absorbed the message that the way for me to stop other people getting angry with me was for me to fix everything, so I'd rush to do that if I spotted any problem of any kind with anyone I knew or came across. It was exhausting and I didn't want this role, but obviously everyone around me loved it and wanted to keep me in it. Since I was doing it unconsciously, I wasn't able to just stop.
It took me moving miles away to make me look around at my life and decide how to live it. I felt I'd done my share of helping humanity and I needed to regroup and focus on myself for a while. So I made a conscious effort to stop being so helpful although remaining kind and sympathetic, at which point the users all disappeared themselves from my life like magic and the penny finally dropped for me about what had been going on.
I knew I wasn't very assertive, looking into that lead me to do lots of reading about boundaries and red flags and I changed my ways dramatically. I'm still there for friends and family and to a lesser extent for strangers, but only when I can do so without being adversely affected myself.