When I stumble upon such discussion I often try not to "put mouth" for the discussion because, it is usually spinner out of context. But permit me to state that "you must not be friends with everyone you come across everyday, but you should be nice even when you have a justifiable reason to be harsh; especially in this space". This is a virtue that is hard to come by for many in this dispensation.
I hardly follow people I cannot engage with unless the contents they share are enough engagement for me. So, If you make your profile public, and can afford to spend time online chatting with your circle, you owe it as a duty to at least, respond to the messages and comments of the people following, even if it will take months due to the overwhelming volume the responses (I can excuse celebrities that recieved volumes of senseless DM from brainless follower making eerie requests). But you see those ones wey no get shi shi and dey form "popular in demand", they are exceptional in ignoring DMs while camping on the DMs of those who just what to "whine" them; forgetting the principles of give and it shall be given. You have not responded to those in your DM but expecting those whose DM you slide to, to respond to you.
People slide into DMs for various reasons and it will be foolish to conclude that everyone is looking for the same things; foolish to judge all with one. It may boil down to the reason why they are in this space. Some people are here just for business and responds to business related DM. Some are here just to connect with old friends and colleagues. Their friends list are made up of people they have share something in common at one point in time. So when you slide into such DMs you will have to first prove your relationship or previous connection with them to get their attention. Others are here to make new and more friends and possibly find love from among these friends, and etc. These ones can be cool headed in responding to DMs.
Although this lady in question appeared polite, but you should also know that when you slide into people's DM and they opens your message, the first thing that most do is to visit your profile and check you out. It is in the process of checking you out that they pick a particular interest in you that they wish to explore. Not because you are a sharp guy that knows how to shoot your shot, or that you 've got vibes, swags and cash, but there is just something about you that interests them that they wishes to explore and they, engaging with you is because of that interest. That is where the crush starts setting in and when there is a crush, you are guaranteed an automatic "Yes" if you can just ask.
Even outside of social media, a lady you met in a bus or anywhere, will engage in a conversation with you and give you her contact; after refusing to do same to like 10 others that have asked her before you and still refuse to 10 more that tried after you who may be far better than you by whatsoever criteria you can think of, only because she picks an interest in you. Most times, this interest is sparked by something about you that many will consider insignificant as to what appeals to a lady and that insignificant thing just happens to be her trigger. There are ladies that have "a thing" for things like cute smile, open teeth, dimple, haircut, eye brow, voice tone, Adam apple, 6packs, etc. If you happen to have "that thing" they have "a thing" for you have won even before make any attempt. It's not just ladies, it's give versa.My advice, sometimes sliding into DMs is like fishing in troubled sea, expect anything.