> Other VPN providers do offer an option of choosing TCP/UDP as per usage i.e. better reliability vs faster speed.
I don't think TCP-based VPNs are offered for increased reliability. They might be offered so you can run your VPN traffic in restricted scenarios, e.g. I run a VPN-ish service that uses TCP/443 by default and all connections are only outbound, so you can still use your VPN in restrictive scenarios.
Outside that, encapsulating TCP inside TCP is nothing short of a headache as you have two congestion control algorithms kicking in and one doesn't know about the other.
I don't think TCP-based VPNs are offered for increased reliability. They might be offered so you can run your VPN traffic in restricted scenarios, e.g. I run a VPN-ish service that uses TCP/443 by default and all connections are only outbound, so you can still use your VPN in restrictive scenarios.
Outside that, encapsulating TCP inside TCP is nothing short of a headache as you have two congestion control algorithms kicking in and one doesn't know about the other.