Amazon's (AMZN 3.43%) rise over the past couple of decades has been nothing short of spectacular. The tech behemoth that seemingly dominates every industry it touches has made for a fantastic long-term investment.

In the last 20 years, the FAANG stock has skyrocketed by more than 8,100%, crushing the broader market and making it one of the best-performing investments during that time. While it's likely far too large now to repeat a gain of that magnitude, the stock is still a solid opportunity.

Here are two reasons you should buy Amazon stock like there's no tomorrow.

1. Exposure to growing industries

Even though it generated $575 billion in net sales in 2023, which is a gargantuan sum, its expansion is far from over. The latest trends show why Amazon is still in full-on growth mode.

In the U.S., online shopping represents under 16% of overall retail spending. Of course, the climb from zero to that level was undoubtedly propelled significantly by Amazon, which now attracts nearly 40% of all e-commerce spending domestically.

It's easy to believe that Amazon will continue to capture a sizable chunk of the industry's growth because its sprawling logistics footprint enables it to provide consumers with a superior e-commerce experience.

Amazon Prime has over 200 million subscribers worldwide. One service it provides is streaming entertainment. Prime Video is the third-most-watched streaming service in the U.S. As its content offerings become better over time, more and more people could flock to the service. And this can translate to greater e-commerce revenue, indicative of how connected Amazon's consumer-facing operations are.

The business also has a booming digital advertising segment that raked in $14.7 billion in revenue in 2023's fourth quarter, up 26% year over year. That puts it right behind Alphabet and Meta Platforms in the U.S.

Many investors might not know that Amazon has such a huge presence in the digital ad market. But because billions of visitors go on its website each month, there's a lot of attention that can be monetized.

We can't forget about Amazon Web Services (AWS). The company's cloud infrastructure unit caters to enterprise and government clients. It reported revenue of $91 billion in 2023, up 13% compared to the prior year.

AWS has unrivaled scale, commanding about one-third of the worldwide market for cloud infrastructure. Being the industry leader gives it an advantage from a profitability perspective. AWS boasted a superb operating margin of 30% in Q4.

But AWS can also gather and analyze much more data than rivals. At a time when the economy is becoming more digitized and there's a growing focus on artificial intelligence capabilities, AWS is able to meet the needs of its customer base. This will only become more evident in the years ahead.

According to an estimate from Grand View Research, the global market for cloud computing will grow to $1.6 trillion by the end of the decade. Given that tailwind, investors can expect AWS will remain a key revenue driver for Amazon's overall business.

2. Attractive entry point

Even after its monumental rise over the past 20 years, investors today have the opportunity to buy Amazon stock at what I believe is a reasonable valuation. While the shares trade just 5% off their all-time high, they are valued at a price-to-sales ratio of 3.2. That's roughly in line with the company's 10-year average on that metric.

Wall Street analysts' estimates forecast that its revenue and earnings per share will rise at annualized rates of 11% and 34%, respectively, over the next three years. Given management's heightened focus on cost-cutting and driving greater efficiencies across the organization, it's not unrealistic to expect Amazon's profits to soar.

Taken together, Amazon's growth outlook and its reasonable valuation make buying the stock a no-brainer decision.