Disney's stock slipped 2% Thursday, despite reporting streaming subscriber gains the day prior, as investors begin to weigh whether the company's massive investment in content is sustainable.

Why it matters: Disney's streaming division still isn't profitable and its losses widened last quarter. Wall Street is worried about whether the company's long-term streaming strategy is most lucrative to investors.

By the numbers: Disney's streaming division, which includes Disney+, Hulu and ESPN+, lost $887 million last quarter, up from $290 million a year ago.

"I'm not sure that's the best use of their capital," senior media analyst Michael Nathanson told CNBC. "I kind of wonder if they set targets themselves that are not achievable or will be too expensive to get there."

Stat of play: Disney on Wednesday said it now has over 200 million paid subscribers across all of its services globally, bringing it a big step closer towards closing in on Netflix's longtime streaming lead.

Be smart: Disney's stock typically trades on its streaming value proposition, even though the company makes most of its money on parks and resorts and its broadcast and cable networks.

The big picture: Netflix's massive selloff last month underscored Wall Street's expectation that streaming services begin to drive profit.

What to watch: The next frontier for growth for Netflix and Disney is introducing an ad-supported tier. Ad-supported tiers can increase subscriber numbers, as well as the average revenue per user.