WhatsApp automatically compresses the photos / images by default which reduces the size and quality of the shared photo / image. WhatsApp / Facebook might have doing this not only to reduce the internet bandwidth of its users but also to reduce the load on their servers.
If anyone would like to share the photo / image without any detail and quality loss they can share the attachment as a document instead of photo / image.
WhatsApp is available on Android, iOS, KaiOS – Mac Web and Windows Web – should connect to the mobile app in more than 40 languages.
Noah Chilamakuri's Blog 