Corporate venture capital was once viewed as an also-ran in the VC game. But tech companies have increasingly large balance sheets and increasingly sophisticated venture arms. Beyond Google Ventures, there’s Intel Capital, Time Warner Capital, and Comcast Ventures. There is increased competition from Asian strategic investors such as Tencent, Baidu and Alibaba. Yesterday, at Fortune’s Brainstorm Tech conference, venture capitalist Jim Breyer noted that corporate VC arms are “competing very effectively” with traditional venture investors.

One tech conglomerate with a lot of cash on its balance sheet but no corporate VC arm to speak of is Yahoo YHOO . The company is set to receive a giant windfall from the upcoming IPO of Alibaba. In addition to CEO Marissa Mayer’s acquisition spree — 41 companies and counting since taking the helm two years ago — why not invest that cash in some startups?

At Fortune’s Brainstorm Tech conference in Aspen today, Yahoo’s Chief Development Officer Jacqueline Reses explained why. It wouldn’t be out of her area of expertise, since she worked in private equity for a decade, but it’s not a fit for Yahoo, because it would take resources away from the company’s already-stretched executive team.

“Yahoo is in a transformation,” she said, “and in order to transform the company, we all need to focus on the things that really matter and drive them to be successful. We need 100% of our attention on our core business.

“Venture investing, to me, is a hobby. If we had the time to have a hobby and we could set up a separate venture arm,” she added. “But that hobby also takes the time of executives… Right now we prefer our executive team to focus on the business and growing that, as opposed to making small investments that we own a piece of.”

Yahoo acquires lots of venture-backed companies, though. When it sees a startup with investment from a corporate venture firm, it’s a red flag. “We always ask, ‘Why are they selling?’ and if its strategic to that company, we ask, ‘Why aren’t they selling to their own sibling?’ and we have to evaluate it thoughtfully.” The information flow can be cause for concern, she noted.

Yahoo doesn’t find itself in competition for many deals — of the 41 it’s done, only a small handful have used a banker, and fewer have had competitive bids. “They come to Yahoo because they want to be part of the company,” Reses said.