Why people on TikTok wanna chat/write with me on Instagram and not on TikTok itself?

Hi, Since like 3 months I'm on Tiktok. Like every second to third day I open the app if I can't sleep or so... I'm not really a content creator, just here and there I upload a photo/video from myself or from my car. I'm 33 years old and I never really was on social media. It's not my world...

But I met a few nice peope there, which have the same car as me, or do funny livestreams or whatever. And they always ask me the same thing; Do you have Instagram, so we can write/chat there.

Then I always say no I don't have instagram. (I mean I have an account, but wasn't on instagram in like 3 years)

So my question is... Why do people on tiktok always ask for instagram and wanna write there? On TikTok you also can write private messages.. And if they really wanna chat or keep in touch with me (more often), ask me for whatsapp or telegram and not for another social media platform😅 Like I said I'm not a content creator. I barely upload anything.

So someone explain this to me. Maybe I'm to old

Thanks