From what I understand, babies may start to drop a nap around this time. As you said, they're more playful and want to explore. Also, maybe not so tired, or getting better sleep at night. I found it really hard to get my son to lie down for a nap once he learnt how to stand up on his own. Sometimes it can be that they don't know how to sit down yet and some books recommend practicing that with them. But with my son even after he learnt how to sit down, he just didn't want to lie down for his nap - he was tired but didn't want to party to end. Forcing him to lie down also was not the answer as he would cry...even the books recommended not forcing them down but just patting their pillow. With my son when he sat down/fell down, I'd pat his back to encourage him to lie down and eventually that worked. Now, we tend to keep him with us on the bed, playing with something or looking out of the window, humming and patting him, and then gently ease him into sleeping position. Not classic sleep training method which recommends getting the child to soothe itself but frankly, this works okay for us.
My son started to drop one nap (1 hour morning nap) when he was a little over 1 year old... but he was still sleeping a good three hours in the afternoon and going to bed at 7.30-8 pm. After his MMR vaccine he was unwell and went back to the morning nap for a week... now seems to be dropping it again. I think it's more common for babies to drop one nap at a time; but as Thanka2 said, there may be some kids that do drop all naps. Gosh, hope my son keeps at least one nap for some more time!