A 10-300mm would be extremely difficult because it combines two very different lens designs in one: ultra-wide at 10mm and telephoto at 300mm. As zoom range increases, designers must make more compromises, especially in image quality.

Main issues:

• optical trade-offs: it becomes much harder to control distortion, sharpness, and other aberrations across such a huge range.
• size and weight: a 300mm lens needs substantial physical length, and if it were made reasonably fast it would also need a large front element.
• slow aperture: to keep size and cost under control, a lens like this would likely need a relatively small maximum aperture.
• handling: large lenses are more awkward and harder to hold steady.
• cost and complexity: more complicated optics mean higher manufacturing cost.
• limited market: consumers often want affordable, compact lenses, while professionals usually avoid extreme-range zooms because they prioritize image quality and speed.

That’s why most high-end zooms have relatively modest ranges, while “superzooms” already make noticeable compromises even around 10x. A 10-300mm would push those compromises much further, making it expensive, bulky, slow, and likely below average optically.