Despite a strong beat on earnings on Wednesday, shares of Fitbit were down almost 15 percent the next day. CNBC's Jim Cramer said he might know why.  "This is one where the numbers were superb, but when we speak with the CEO, you can't run your company like a private company when you're public," Cramer said on Thursday on CNBC's "Squawk on the Street."  "You can't say 'stay tuned' when people ask you how things are going."  Read MoreFitbit shares sink 15% despite strong first report  Cramer was referring to the conference call in which Fitbit CEO James Park did not give specific answers when asked questions about the performance of his company.  "We won't release a product before it is ready," Park said on the call. Investors were looking for hints on new product plans for the wearables maker.  Fitbit reported it had sold 4.5 million wearable fitness devices in the quarter, up from 1.72 million in the year-earlier period. Fitbit's gross margin came in at 47 percent, also worrying some investors and contributing to the stock decline.  "This was a fabulous quarter, there's no flies on it," Cramer said. "But companies have to play by the rules or their stocks suffer on a great quarter."  Read MoreFitbit investment spending is driving growth: CEO  Speaking on CNBC's "Squawk on the Street" earlier on Thursday, Park said, "It's important to note on the gross margin side it was well within guidance."  He then went on to attribute the decline to a stronger dollar and increasing capacity for its best-selling product.  "The market itself is not well defined in terms of the actual growth rate," said CSLA analyst Ed Maguire. "It's very easy for expectations to get well ahead of themselves."  Maguire, who spoke on CNBC's "Closing Bell" Thursday, also said that the wearables market is highly competitive and "how this ultimately plays out is going to be subject to a lot of forces."  —CNBC's Jacob Pramuk contributed to this report.  Disclosures: Neither Ed Maguire nor CSLA owns shares of Fitbit.
CNBC's Jim Cramer discusses why Fitbit's stock sank despite a beat on the top and bottom line on Wednesday.