People are Neglectful to it
Sayyiduna Usama Bin Zaid said, I asked ‘Ya Rasool ALLAH (May Peace and blessings of Allah be upon him)! I see that you observe fasts more (extensively) in the month of Shaban than any other month.’ The Holy Prophet (May Peace and blessings of Allah be upon him) replied, ‘It is a month Between Rajab and Ramadan; people are neglectful to it. In this month, the deeds of people are ascended towards ALLAH and I love that my deeds be ascended in a state when I am observing fast.
(Sunan Nasai, pp.387, Hadis 2354)