It's a feature: history synchronization between different devices and fast search through hundreds of thousands of messages is, for most uses and users, more important than concerns that Telegram or nation-state level attackers (one capable of silently breaching Telegram infrastructure) would choose to read your chats.
Signal also does historical synchronization between devices. It bootstraps the history from another device. It also has search which can be done locally. Telegram is, by design, capable of being accessed by 3rd parties (beyond governments). iMessage is capable of being accessed by 3rd parties via iCloud backups, which is an opt-in situation.
Be aware, wechat sends every message with geolocation to the authorities in real time. It is more critical than ever that we be aware of the mechanisms in the systems we build and use -- else dystopia awaits.
It's a feature: history synchronization between different devices and fast search through hundreds of thousands of messages is, for most uses and users, more important than concerns that Telegram or nation-state level attackers (one capable of silently breaching Telegram infrastructure) would choose to read your chats.