Of course it can be a choice. But, as with all choices, sometimes we like to imagine that outside pressures had less to do with our decisions than they really might. If I had been brought up to accept the hijab as part of my identity and the act of covering as part of my value, I'd choose to cover, too. Same probably goes if my family/peers held a higher opinion of me for always wearing the hijab. I'd probably like to hang on to that status. Or, as was designed, if I thought I'd be increasing or decreasing my chances of being rewarded by a very nit-picky god. Not all women will be in that situation, but I'd imagine more than you'd ever hear admitting it or even acknowledging it to themselves.
I'm still somewhat struggling with this as far as modest clothing goes. I try to wear long skirts, or, increasingly nowadays, skirts as low as knee-length when I go out. Now, on one hand, if you ask me why, I'll say it's a decision. And it's true that it's a decision. The husband doesn't force me, no body forces me. I buy my own clothes, I choose my outfits in the morning. And I do feel more comfortable on the modest side.
But then if you or I kept prodding myself over why
I was making this decision, then I'd have to start saying, if I were being honest, that it is because I'm trying not to push my husband's comfort level any farther than I have since my apostasy, that I had gotten so used to this clothing, that I have apprehension about being seen by other Muslims in anything more stunningly immodest than the lower half of my legs showing, that I already actively avoid places on campus and in the town where I might run into and thereby disappoint old Muslim friends and mentors. So, today, I decided to dress modestly.