By now, most investors have heard that Apple (AAPL 1.28%) blew the lid off its quarterly earnings estimates. Apple reported a monster quarter in late April, fueled by record second-quarter iPhone and Mac sales, as well as record performance of the App Store.

And yet, Apple's stock price is actually down since its earnings report. Investors may be asking how this could be possible, given that Apple revenue and profit soared last quarter.

Here are two things from Apple's report that should concern investors and which may explain the stock's poor performance since earnings.

iPhone concentration increases yet again
The first glaring issue facing Apple is how much it depends on the iPhone. It's certainly true that Apple offers a number of products outside its smartphone, including the iPad, Mac, App Store, and Apple TV. But these secondary devices and services make up a small part of Apple's business, even when grouped together. Last quarter, Apple raked in $40 billion in iPhone sales. No other Apple product collected more than $5.6 billion in revenue.

The iPhone represented 69% of Apple's total revenue, up from 57% in the same quarter the year before. This doesn't seem like a bad thing at all, since iPhone revenue jumped 55% year over year. But put differently, if the iPhone ever loses prominence with consumers, Apple doesn't have much room for error. This is a concern, since the smartphone industry is highly competitive.

Moreover, Apple's second most important device, the iPad, is in a dangerous decline. Revenue from the iPad collapsed 29% last quarter, year over year, and the iPad now generates less revenue than the Mac. It seems that the big-screen iPhone 6 Plus fits the mold of a "phablet" and this may compel customers to get by with just an iPhone, and be less incentivized to buy both an iPhone and an iPad.

Apple is in the process of unveiling new products designed to widen its revenue streams. The most important of which is the Apple Watch. But Apple's smartwatch is still in its infancy. The company did not release sales data for the Apple Watch in its quarterly earnings release, so investors should keep a close eye on this going forward.

Dividend increase was a disappointment
The other lingering concern from Apple's quarterly report was its subsequent capital allocation announcement. Apple announced a brand-new $200 billion capital allocation program, which will be utilized through May 2017. This is a huge amount of money to funnel back to shareholders, but the majority of it will be accomplished through share buybacks. This leaves dividend investors out in the cold.

Apple did raise its dividend by 11%, which for many companies, would be a strong raise. But even with the increase, Apple stock yields just 1.6%. Apple needed to increase its dividend by a much higher rate to bring it on par with other dividend-paying technology stocks like Microsoft (2.6% yield)and Qualcomm (2.8% yield).

Plus, Apple's fundamentals more than justified a greater dividend increase. Apple generated more than $47 billion of free cash flow in the first half of its fiscal year. In that same period, the company paid just $5.5 billion of dividends, which equates to a minuscule 11% free cash flow payout ratio.

Possible explanations for Apple's sell-off
The fact that Apple's stock has declined rather significantly since its earnings and capital allocation announcements is a telling sign that the market didn't love the company's decisions. Clearly, the iPhone is a smash hit right now, thanks to the fabulous performance of the iPhone 6. But it may not always be this way, and since the iPhone is Apple's most important product by far, Apple is in danger of being a one-trick pony.

Separately, Apple's capital allocation program is heavily geared toward stock repurchases. Buybacks are all the rage these days, but after a 50% rally in just the past year, Apple's buybacks are less accretive to earnings.