It's because they use JavaScript. Even if you visit the clearnet link and disable JavaScript from your browser settings, you will get a blank page (Your Tor settings are probably set to disable JS).
So that means they are going against their own reccomendations on their "Step-by-step guide on how to mix your coins" article?
Assuming these coins are going to be sent to a darknet market… if you don’t already have your deposit address, sign in and get it while having JavaScript disabled. Never use any market that requires you to enable JS!
Regarding the reference to the dark market and the Russian evading state regulations example: MCM may be considered a money transmitter under FINCEN, which means they'd need a license:
https://cryptobriefing.com/bitcoin-coin-mixers-legal-crosshairs/"Users of mixing services, however, need to be more vigilant. They are liable, according to FinCEN guidance, of being found to be intending to conceal the identities of funds or are, in fact, operating as transmitters. Transmitters need licenses. Concealing the identity of a sender or receiver of funds is a breach of the Funds Travel Rule if conducted by a registered financial institution.
While non-custodial wallet developers are not in breach of any legal obligation, those who use their software could be. The concern for those using mixing services is that in both the Harmon and Bestmixer cases, the enforcement actions were premised on the intent to conceal dirty Bitcoin.
Perfectly valid privacy-based grounds for mixing cryptocurrencies risk being swept up in the zealous delivery of law enforcement. Even if the primary purpose of this software is to protect people’s identities, there may be a tendency for law enforcement to assume these coins were ill-gained."