Loosing weight v's loosing and being healthy?

I'm going to start by saying that i am not going to change the way i am doing things now, I'm just making a comparison.
So before christmas i started the new pro points system and lost 12lbs in about 5 weeks, didn't do any exercise with it really, just the odd walk nothing major, i ate what i wanted just within points. certainly wasn't eating clean and had cheat days once a week which was within points. Obviously i put that weight back on over xmas and the following months.
So here i am now, about 40ish days into mfp, I've completly changed the way i eat, i eat mostly home cook, wholegrain foods, much more healthy! I also exercise atleast 5 times a week, cardio and weights and i've lost 7lbs in the same space of time.
When i was at this weight the last time i was in smaller trousers, This time my thighs and hips do not want to shrink at all! although my stomach is flatter, my arms are much stronger and defined and my waist is decreasing!
I just wondered why loosing weight can differ so much from one time to the next? Why sometimes it comes from one place but not the next. why exercise seems to have made a difference to my weight loss and body shape in comparison to the last time?

Like i say i'm not really complaining about this, it's merely an observation about how things have gone for me in the past. I am happy to loose weight how i am, i am much fitter and healthier.