Why photos lose quality
Most photos do not look bad because the camera itself is bad. Quality usually drops because of missed focus, camera movement, heavy JPEG compression, poor lighting, or an original file that is simply too small. A phone can capture a good scene and still produce a soft image when the subject moves or the light is weak. Images downloaded from social networks can also lose detail after repeated compression.
Normal resizing does not solve this problem. It stretches the pixels already present in the file. The dimensions become larger, but edges, hair, skin texture, fabric, and small objects do not become genuinely clearer. The photo often ends up bigger and softer at the same time.