As the rich get richer, they are also branching out. They are muscling aside or buying out rivals. And they are locking in the industry’s best engineers with paydays smaller companies could never match.

Amazon said last week that it had invested in the infrastructure needed to speed up shipping times for its Prime members to one day from two, raising the bar even higher for retail competitors. But Monday’s trading on Wall Street showed just how hard it is to stay in the trillion-dollar club. Despite its e-commerce and cloud-computing dominance, Amazon’s value dipped just a bit below $1 trillion.

Apple recently earmarked billions of dollars to create shows and movies for its video subscription service in a challenge to Netflix, while Alphabet agreed to buy the activity tracker Fitbit for $2.1 billion in November and the analytics software firm Looker for $2.6 billion in June.

“Today’s dominant companies have so much power across such a broad array of markets and continue to leverage that power to expand into new markets,” said Patrick Spence, chief executive of the speaker maker Sonos, at a congressional antitrust hearing last month in Boulder, Colo.

Sonos has sued Google, accusing Google of infringing on five of its patents, including technology that lets wireless speakers connect and synchronize with one another.

Tech’s richest companies seem to be defying a Wall Street assumption that as a company gets bigger, it becomes difficult to find new ways to make money and maintain rapid growth. Alphabet said profits in the last quarter of 2019 were 19 percent more than a year earlier. Revenue rose 17 percent to $46.1 billion, slightly below Wall Street expectations. The company’s stock fell 4 percent in after-hours trading

To assuage some concern about sluggishness in its main search ad business, Alphabet disclosed for the first time detailed revenue figures for its YouTube and cloud computing units, which are growing faster than the rest of the company. YouTube sold $15.1 billion worth of ads in 2019, up 36 percent, while its cloud unit grew more than 50 percent to $8.9 billion. Ad revenue from search increased 15 percent to $98.1 billion.