By Anna Tong, Aditya Soni and Deborah Mary Sophia(Reuters) -Big technology companies including Microsoft (NASDAQ:MSFT), Meta (NASDAQ:META) and Amazon (NASDAQ:AMZN) are stepping up spending to build out AI data centers in a rush to meet vast demand, but Wall Street is hungry for a quicker payday on the billions invested.Microsoft and Meta both said on Wednesday their capital expenses were growing due to their AI investments. Alphabet (NASDAQ:GOOGL), too, reported on Tuesday that these expenditures would remain elevated, while Amazon said they would increase the rest of the year and into 2025.The extensive capital spending could threaten fat margins at these companies and pressure on profitability is likely to spook investors.Big Tech shares fell on Thursday, highlighting the challenges the companies face as they seek to balance ambitious AI pursuits with the need to reassure investors they are focused on short-term results.Shares of Meta slipped 4% and Microsoft fell 6%, despite each topping profit and revenue expectations for the July-September period. Amazon fell 3.4% but investors sent the shares up aftermarket on better-than-expected third quarter results."It's costly to run AI technology. Getting capacity is expensive," said GlobalData analyst Beatriz Valle."It has become a competitive race among the big tech companies to build out capacity. It's going to take time to see the returns, to see widespread adoption of the technology."Amazon on Thursday said it expected higher capital expenditures for the foreseeable future to help serve the development of AI software. CEO Andy Jassy in a call with analysts called AI a "maybe once-in-a-lifetime type of opportunity."investing.com