Why would Hermione and Harry smell things that reminded them of Ron and Ginny in the love potion?
So, Amortentia or “Love Potion" is described to smell like things or people the smeller loves.
Hermione, at least in the movie, states that she smells new parchment, freshly mown grass, and…(she grows quiet)… spearmint toothpaste. The toothpaste is a reference to a scene earlier in the film where they are all at the Burrow. Hermione had just brushed her teeth and still had some toothpaste on her face. Ron pointed this out to her and (quite adorably) brushed it off her face with his finger.
It's a common trope in romantic stories. “Hey, you got something on your face, let me get it for you.” It's used as an excuse to touch your love interest’s face and to get closer to them, and, possibly, even get a kiss out of it.
In the book of Half-Blood Prince, Harry describes smelling treacle tart, a broomstick handle, and “something flowery he thought he might have smelled at the Burrow". (Chapter 9, pg. 183)
That flowery smell is later revealed to be Ginny’s hair.
Hermione says the following on page 185: “…and it's supposed to smell differently to each of us, according to what attracts us.”
Slughorn explains, “Amortentia doesn't really create love, of course. It is impossible to manufacture or imitate love. No, this will simply cause a powerful infatuation or obsession. It is probably the most dangerous and powerful potion in this room… When you have seen as much of life as I have, you will not underestimate the power of obsessive love…”
Romilda Vane gives Harry spiked Chocolate Cauldrons for a Christmas present. He throws them away from his stuff, but Ron finds them and eats them. He becomes obsessed with Romilda (which is awkward because he is still dating Lavender Brown at that moment) and is unable to think clearly.
Eventually, he is cured, but it’s a great example of how a messed up love potion can make someone.
TL: DR; Harry and Hermione are definitely infatuated with Ginny and Ron, respectively, and so that's what the Amortentia smells like to them. However, you are correct Amortentia does NOT create real love and instead of an obsessive attraction to the person, as we can see with Ron eating a love-potion spiked candy from Romilda Vane.