Telegram does not refuse take down content. I have reported scams, phishing, selling stolen credit cards and such to Telegram and they have all taken down. Maybe not in 24h, but still taken down.

Also from your study: “Our investigation finds that large networks of accounts, purportedly operated by minors, are openly advertising SG-CSAM for sale on social media. Instagram has emerged as the primary platform for such networks, providing features that facilitate connections between buyers and sellers. Instagram's popularity and user-friendly interface make it a preferred option for these activities.”