It's actually almost unbelievable that you can browse endlessly and never once be prompted to sign up unless you try to engage in some way.
This is the typical freemium cost structure amped up because endless video streams for the free (anonymous) tier resulting in higher peak-load operating costs (bandwidth & compute). In exchange, TikTok enjoys higher virality which they hope will translate into higher aggregate (but lower relative percentage) sign-up conversion rates.