TL;DR: No, smartphones aren't inherently less secure than PCs. They are just more valuable to target, and generate more media attention.
In fact, smartphones are arguably more secure than PCs. They restrict all applications to an often restrictive sandbox, and require the apps to request permissions for access to basically any resource. Compare this to PCs, where practically all applications have access to essentially everything. (Obligatory XKCD). Additionally, modern smartphones often have much better physical security measures than many PCs.
Smartphones produce much more bang for the buck.
A fully compromised smartphone is will give access to practically all of a target's communications: their phone calls, SMS messages, encrypted text messaging (Signal/WhatsApp/iMessages) and probably their email as well. You will also gain access to a good portion of their web browsing, and their is a very good chance you will gain access to their 2FA as well (Authenticator application or SMS) allowing you to further easily compromise any of their online accounts. Plus, you gain access to any files on their phone (which are often very good kompromat if your goal is to blackmail), their live location and the ability to spy on them covertly through the camera and the microphone.
Compare that to a laptop. You gain access to some of their web browsing, some files (often only professional in nature), and maybe access their camera and microphone some of the time, since the laptop isn't always on and besides you, and a lot of people cover the camera on their laptops.
Smartphones are easier to covertly exploit
A smartphone generally has a larger attack surface directly exposed/accessible from external networks. All you need is a zero-click vulnerability in any of the messaging applications that a target is known to use, and their phone number. This exploit will pass through any firewalls or NATs on the device.
With a PC, it gets more difficult. Generally, a PC will be sitting behind a NAT, so its network stack cannot be attacked directly. And often the only application a target will be using to access the internet is the browser. This means that most exploits will require the victim to click on a link or download and open a file. This can easily raise suspicion, resulting in the exploit getting caught prematurely. A PC is also much more likely to be running security software like Anti-Viruses, again increasing the chances of the exploit getting caught.
Economies of scale
Economies of scale apply much better to smartphones than PCs. Everybody is using the same phone (the vast majority of valuable targets will be using an iPhone) running the same handful of applications. Once found, one zero day exploit chain can be used against a large number of targets.
In contrast, laptops/PCs will be running a larger variety of operating systems with different configurations, and an even larger variety of targetable applications (browsers, mail clients, pdf readers etc), making it much more difficult to develop an exploit that will work against pretty much everyone.
All of these reasons add up to making it much more cost effective for exploit vendors to develop exploits against smartphones. That's not to say PCs are less vulnerable or that exploits targeting them are rare. In fact, based on data from Project Zero, the number of zero days found in the wild in 2021 targeting desktops outnumbers those for smartphones (28 vs 19).
