This is an honest question, no judgement. Maybe a handful of dead flowers makes perfect sense to some people. It just seems like there are so many better ways to say "I love you!" or even "you're decent!" than some mutilated plants. Chocolate is great, back scratches are great, a bottle of wine is very great, some sad murdered roses... whatever floats your boat, I guess...?
Perhaps at first those flowers could fill the hole in my chest; their luscious petals might cushion out the gap and make me feel momentarily content. However, as it is with plants hacked from their roots and forced to suck down chemically enhanced tap water, they will quickly wither and thus open the hole anew leaving only a sad, wrinkled corpse and a displaced flower spirit. Then, I will just be empty AND haunted.
You might be getting clever and thinking, "Well chocolate and wine are finite as well!" and this is true, however, they leave good feelings in their wake. Their mass is replaced by the pleasure they carry, whereas flowers just leave behind the reminder of inescapable death and decay.
Okay, okay, I get it, you just want to have your silly little holiday with some light-hearted quasi-romantic fun and I'm raining on it with talk of death. It's totally fine if this martyr's namesake holiday inspires you to spend money on cheesy cards and grocery store bouquets for your main squeeze. Meanwhile, I'll be looking for the special someone that buys me something that says "You're someone I think about sometimes" and actually lasts!