Warren Buffett is buying. He and his investment managers have bought 18 stocks for Berkshire Hathaway's (BRK.A 0.64%) (BRK.B 0.54%) portfolio so far in 2022, plus major buybacks of Berkshire itself. Buffett and his team scooped up shares of eight companies in the third quarter alone.

But Amazon (AMZN -1.14%) wasn't in the group. Sure, Berkshire maintains a relatively small position in the e-commerce and cloud hosting company. Despite the stock's steep decline this year, though, Buffett hasn't even taken a nibble on it.

Why isn't Buffett buying Amazon hand over fist right now? I suspect there are three main reasons.

1. Better bets

The obvious explanation for why Buffett isn't buying Amazon is that he thinks there are better bets. If he felt otherwise, he would have no doubt added to Berkshire's position in the company already this year.

With the lone exception of Apple, all of the stocks that Buffett has bought so far this year are much smaller than Amazon. Why is this important? It's harder for a company with a market cap of close to $1 trillion to grow than it is for a smaller company to do so.

Buffett likes Apple so much in large part because he knows that the company's iPhone ecosystem is sticky. This gives the company a strong moat, something the legendary investor really appreciates. 

I suspect that he's not as sold on Amazon's moat. The company is certainly the 800-pound gorilla in e-commerce. But it has increasing competition from the likes of Walmart and Shopify. Amazon Web Services (AWS) reigns as the leader in cloud hosting, but Alphabet's Google Cloud is gaining ground quickly.

2. Valuation concerns

Buffett isn't as much of a purist with value investing as his mentor Benjamin Graham was. Make no mistake, though: Valuation matters to him.

It wouldn't be surprising if valuation concerns are a key reason Buffett hasn't bought more Amazon shares. The company is notoriously difficult to value.

Amazon reinvests so much of its profits that you can pretty much throw earnings-based valuation metrics out the window. Discounted-cash-flow models are challenging for the company as well because its free cash flow has fluctuated wildly in recent years.

Buffett acknowledged in the past that Amazon was one of the stocks that were "outside my circle of competence of evaluating." He didn't even initiate Berkshire's position in the company; one of his investment managers did. 

3. Near-term headwinds

I doubt that anyone would refer to Buffett as a market timer. He has consistently advocated a long-term perspective and practices what he preaches. But that doesn't mean that he wouldn't stay away from a stock that had near-term headwinds. There's no question that Amazon has its fair share of such headwinds.

The strong U.S. dollar is weighing on top-line growth. Management's outlook for the fourth quarter was weaker than expected. Macroeconomic uncertainty is causing AWS customers to tighten their belts. The company continues to feel the impact of high inflation. Perhaps the single biggest concern for Amazon right now is that its free cash flow has plunged into negative territory. 

Would all of this keep Buffett away if he liked Amazon's long-term prospects and wasn't worried about its valuation? Probably not. However, it could still factor into his decision at least a little.

A big assumption

I'd be remiss in not mentioning that I've made a big assumption so far. That assumption is that because Buffett didn't buy Amazon stock during the first three quarters of 2022, he's not buying shares now.

If I were Buffett, I wouldn't let Amazon's near-term headwinds affect my thinking. The company's issues are only temporary ones. I wouldn't be put off by the stock's valuation, either. On the other hand, I'd tend to agree that there are at least a few better bets than Amazon.

But I nonetheless believe that it is still a really great stock to buy right now. And if I had the $100 billion or so that Buffett has at his disposal, I'd be sorely tempted to back up the truck and load up on Amazon. Maybe, just maybe, we'll learn in the not-too-distant future that Buffett has been doing just that.