To put things another way, security measures generally are only good for buying time. The amount of time bought generally negatively correlates with the amount of resources spent by the attacker. This is not always the case, for example a message encrypted with a one time pad will never be decrypted unless the key is compromised. However, in the majority of cases a security measure can only buy time even if it is properly implemented. In the case of strong encryption such as AES, the amount of time bought is more than enough. It is so long that the universe will die prior to the amount of time bought running out. An attacker can spend enormous amounts of resources trying to reduce the amount of time bought, but even if they spend trillions of dollars they can not reduce the amount of time bought to a level that makes it practical to spend resources. In the case of anonymity networks, especially low latency anonymity networks, the amount of time bought is much less. It might be measurable in hours or days instead of millenniums. Or it might even be measured in weeks or months or years. And attackers are much more capable of reducing the amount of time to practical levels. If you halve ten billion years you still have five billion left. If you halve a year you are left with six months. Even most high latency solutions can only provide anonymity for a number of messages (against global passive attackers). Maybe they will allow you to send fifty messages before you are identified, perhaps one hundred. Exact numbers aside, the point is simply that even rather strong anonymity systems are simply not comparable with strong encryption systems in regards to the amount of resources that it takes for an attacker to compromise them in a practical amount of time.