Because like every other scene in the book, the love scenes need to move the plot forward, reveal something about the characters, as well as explore the emotions involved in such a deeply personal act.
So let's be specific. Let's say my heroine is looking at the hero.
He was gorgeous. Even the sick yellow sodium streetlight couldn’t erase his high cheekbones and navy blue eyes. His full lower lip summoned her to kiss and bite. His worn shirt framed his chest and rippled belly. Lost in a fog, she barely registered licking her lips when she saw a line of flesh above the waistband of his low-slung jeans. One long fingered hand touched the glass as he leaned in closer, his eyes locked on her.
The world shrunk. Those strong, scarred digits slid, lazy and slow, down the window. His thumb hooked through his belt loop. He cocked his hip in masculine invitation to look and appreciate. The grace of him sent an unfamiliar shudder through her breasts. Its power rocked her back on her heels. In all her long life, had she ever felt an erotic blow like this? Her body wanted to know how those fingers would feel.
What makes this snippet work or not isn't the description of his body, delightful as it is. It's what she feels, the emotion that the visual brings to her. Her desire, surprise, and yearning tell you that she's sexual, though she's not been intimate, not just physically but also emotionally, with someone for a very very long time.
