As we traverse the trajectory of the 21st century, mobile technology continues to infiltrate every facet of our lives. The crystalline presence of mobile applications, in particular, has reimagined our interaction with digital platforms, transforming our smartphones into Swiss Army knives of utility. As such, the companies that develop these applications are of critical importance in shaping the future of mobile technology.

The landscape of mobile app development has been marked by constant evolution. From the initial days of native app development to the advent of hybrid and progressive web applications, the mobile app industry has seen numerous technological shifts. Each of these shifts has come with their respective merits and demerits. For instance, while native applications offer superior performance and a seamless user experience, they necessitate separate development efforts for different platforms, increasing both cost and time. On the other hand, hybrid and progressive web applications allow for cross-platform development, albeit at the potential expense of performance and user experience.

Given this historical context, it is important to consider the trajectory that mobile app development companies might embark upon in the future. In contemplation of this, one must consider a confluence of technological advancements, market trends, and demographic shifts.

Artificial Intelligence (AI) and Machine Learning (ML) are among the most promising technological advancements that will significantly shape the future of mobile applications. With capabilities such as predictive analytics, personalized user experience, and advanced automation, AI and ML will offer mobile app development companies new avenues to explore and exploit.

Moreover, the advent of 5G technology promises to revolutionize mobile applications by providing unprecedented speed and lower latency. This enhancement will enable the development of applications that require real-time data transmission such as augmented reality (AR) and virtual reality (VR) based applications. In addition, the reduced latency will improve the efficiency of applications that rely on cloud computing.

From a market trend perspective, the increasing demand for personalized user experiences is a significant driver of change. Personalized user experience is no longer a luxury but a necessity as consumers demand applications that adapt to their preferences and usage habits. This trend is expected to continue, with companies investing more resources into data analytics, AI, and ML to make their applications more personalized and intuitive.

Equally significant is the demographic shift towards a younger, more tech-savvy population. This digital-native generation has grown up in an era of smartphones and applications, and thus, their expectations are substantially different from preceding generations. They demand applications that are not only functional but also engaging and interactive.

To meet these diverse demands, mobile app development companies need to adopt a more user-centric approach. This requires a deep understanding of the user's needs, preferences, and behavior, and the ability to translate these insights into the design and development of the application.

To sum up, the future of mobile app development companies will be shaped by a plethora of factors, ranging from technological advancements in AI, ML, and 5G, to market trends around personalized user experience, and demographic shifts towards a more tech-savvy generation. The ability of these companies to adapt to these changes, while maintaining a user-centric approach, will be critical in determining their success in this ever-evolving landscape.

In the grand scheme of things, the only predictable aspect about the future of mobile app development is its unpredictability. However, by embracing change, and staying abreast with technological advancements and market trends, mobile app development companies can position themselves to be at the forefront of this dynamic industry. After all, the future belongs to those who prepare for it today.