As Apple prepares to show off new features for the iPhone and other devices at its developer conference on Monday, the company is grappling with an uncomfortable issue: Many of its existing features are too complicated for many users to figure out.

At last year's conference, for example, Apple's top software executive, Craig Federighi, demonstrated how users could order food, scribble doodles and send funny images known as stickers in chats on its Messages app. The idea was to make Messages, one of the most popular apps on the iPhone, into an all-purpose tool like China's WeChat.

But the process of finding and installing other apps in Messages is so tricky that most users have no idea they can even do it, developers and analysts say.

DoorDash, a US food-delivery app that Federighi displayed on stage as a model of the new feature, dropped its Messages app for group orders a few months after releasing it because it drew little interest.

"While we didn't end up moving forward with it, we're excited about other ways we're making delivery faster and more efficient," Andy Fang, a founder of DoorDash and the company's chief technology officer, said in a statement.

A similar lack of enthusiasm among users and developers has limited adoption of the iPhone's 3-D Touch feature, where a long, hard press on an app sometimes offers additional options such as viewing an email without opening it. And sales of the Apple Watch have been hampered by the steep learning curve it requires of users, who must master pushing, turning and tapping various parts of the watch and a related iPhone app.

"There's just so much stuff," said David de Min, chief executive of Velapp, a startup based in London. "They are trying to cram things in."

Velapp has just released a video recording app that uses 3-D Touch to help users select the best parts of a video while recording it. But de Min said that few other developers were using the technology, in part because iPhone users were unaware of it. "It's not something you can really see," he said. "People don't understand it."

Apple, which declined to comment for this article, makes many updates that are popular with users, from changes to the Siri voice assistant to automatically transcribed voicemail messages.

At this year's Apple Worldwide Developer Conference in San Jose, California, the company is expected to introduce improved Mac computers and iPads, software updates for all of its hardware and a voice-activated speaker to compete with Amazon's Echo and Google's Home.

With Apple adding fewer major features in recent years, customers have been slower to upgrade their devices.

App developers are also pausing in what had been a race to embrace Apple's latest innovations. Eliran Sapir, chief executive of Apptopia, an analytics firm, said that new apps were being introduced at half the rate they were a year ago.

Apple TV apps are hot, he said, but developers are fleeing Apple Watch. "There is no way to monetise the watch whatsoever," he said.

The slow uptake of apps for Messages and 3-D Touch is evident in the numbers.

There are 5,000 regular apps and 30,000 sticker apps for Messages, according to Randy Nelson, head of mobile insights at Sensor Tower, an app analytics firm. Only about 3,600 of the 2.5 million apps in the iOS app store promote their compatibility with 3-D Touch.

"You get your new iPhone and you don't know that 3-D Touch and apps in Messages even exist," Nelson said. Although stickers account for 97 of the top 100 Messages apps, he said, some users are so confused that they post app reviews like, "I downloaded these Disney stickers. How do I use them?"

That is not exactly in line with the simple "it just works" philosophy that Apple built its business on.

Chalen Duncan, a graduate student in emerging media at the University of Georgia, was so frustrated by the interface for stickers and apps in Messages that he redesigned it and posted his version online.

"At its core, it's a discoverability issue," said Duncan, who worked part time on Apple's telephone tech-support team during college and hopes to get a design job there in the future. "People just don't know the stickers exist."

He said he had to teach his friends how to install and use Messages stickers by sending them multiple screenshots.

"A lot of people will think it's their fault, and it's really the designer's fault," he said. "People want apps to be easy to use."

The New York Times