Relationships are meant to be built upon trust and loyalty, if you keep that at the forefront of your mind, you're less likely to deceive your partner.
Unfortunate as the case maybe, there is always going to be those that fail to maintain that of trust and loyalty and it starts out as a little white lie, then another one is needed to cover that one and so it continues until eventually you've lost that bonding unless you nip it in the bud and own up to it despite risking what you have, better to come clean than continue down the same road.
Umm I realize this is an old forum and no way shape or form am I trying to be catty but you're beautiful, you don't need to wear a negligee in your profile picture. You might be attracting the wrong attention and they may not take you seriously. I would feel the same if a guy's profile picture was of him shirtless and wearing booty shorts in a seductive spread eagle pose. Well I would probably think two things.
If they feel judged or don't want to start a fight over something they deem harmless. To avoid confrontation and get away with flirtatious or other actions that aren't appropriate when in a relationship, and because they're not fully invested in a future with you or on the flip side to save someone from being hurt based on a mistake they made or other regrets.