I used not to understand why so many women care about getting flowers from their boyfriends/husbands - or, really, to understand people at all - but here's what I've learned. Maybe someone else can learn it the easy way, by just being told the rules.
If you are socially adept at all, you are constantly looking for cues that someone likes or dislikes being around you, whether you notice it or not. Imagine you were having a conversation with someone and they didn't respond to your statements, and responded to your questions with the minimal possible semantically appropriate answer:
You: "How are you?"
You: "Did you see the new Superman movie?"
You: "I was disappointed at how they Batmanned it up."
You: "I mean, Superman is supposed to be an optimistic story."
You: "Looks like it might rain later."
Does it sound like this person wants to have a conversation with you? No, it does not. When someone is interested in conversing with you, they will riff off of what you're saying, respond to a conversational provocation with a new thought of their own, and take questions as an opening to talk about something they care about. When they're not interested, they will try to keep the conversation as short as possible, and give you no openings to extend it.
It's the same on the relationship level. If you want to be friends or romantic partners with someone, the normal thing to do is to suggest ways to spend time together, and either accept their invitations or suggest alternatives. You will accept some suggestions even if they're not things you'd normally do, because they are pretexts to hang out with the other person.
There is another type of conversational cue, non-verbal in nature. If someone is talking to you and you are interested in what they have to say - or if you want to get along with them and have a conversation even if they happen to be talking about something you don't particularly care about - the normal thing to do is to nod, possibly make affirming noises or gestures, and look at them. In romantic relationships, things like a man buying a woman flowers are equivalently socially normal signs that one is interested and wants to continue.
If you were having a conversation with someone, and they made no affirming gestures, but just looked at you with a blank face, you'd ask them what was wrong. And even if they assured you that they enjoyed your company and wanted to continue the conversation, it would still feel weird and unsatisfying.
If you are a man and you are dating a woman who has been taught that flowers are a normal way of expressing affection, and you don't give her flowers, it can feel every bit as weird and unsatisfying, even if you assure her that you enjoy her company and want to keep spending time with her. It doesn't really feel like someone likes you if they don't give you the normal social cues that they like you.
Of course, since there is more than one woman, not all women are the same or want or expect the same things. And of course you the reader might not be a man dating a woman - or might be trying to work on being a better friend instead of a better boyfriend. The concept of love languages is actually a really useful one here, and the gist of it is that different people expect affection to be shown in different ways. So what you actually have to do is pay attention.
If someone lights up when you give them a gift, but not when you hug them, then you need to get into the habit of giving them little gifts, even if you wouldn't feel good if you got them, because you naturally express your affection with touch - in that case, you have to figure out that what it feels like to you to get a hug, it feels like to them to get a physical object as a token of affection. The point is, your relationships will get a lot better if you start paying attention to what the other person cares about, and accept that as a fact about the world. It doesn't matter what seems like it should make the other person feel good, or what feels to you like a genuine expression of affection - the only thing that matters is what actually works. The thought doesn't count until you've learned the other person's language.
On the other hand, when you learn how someone else differs from you, you may also learn something about yourself, and be better able to articulate and express your own needs (which is also something a lot of people need to become more comfortable with - more on this in a future post). And you may start noticing that someone else is trying to express their affection for you much more than it seemed before - once you can understand which behaviors they personally find emotionally salient.