in my opinion sellers can communicate better with customers via telegram.
one of the great features of the Instagram is stories, telegram add stories lately,telegram have bots, channels, mini-apps so you can have better tools to sell your products.
telegram have an internal ads feature, beside that there is other ways like advertising in popular channels, groups and bots. many people already use these kind of advertisements in Telegram.
Anecdote: Both my parents and all grandparents have Telegram while none of them have Instagram.
It's a chat app used by a much wider audience than Instagram. Instagram is predominantly used by younger people who want to live the digital social life.
Where are you based? In the USA I don’t know anyone using telegram. I only recently downloaded it to follow some channels related to the Israel/gaza conflict. I really like the app.