Deceptive recruiting or "staged" commitment
No one would join a cult if they were given a contract stating all that would be expected of them if they become a member. So the potential recruit is most often presented with a nice façade (a whitewashed sepulchre, if you will) that bears no resemblance to real life in the group.
Some groups (especially those that prey on the military) will actually admit this behavior, claiming that they are "no different from the military." "You didn't know what you were in for when you enlisted, and living for God is just like that." While there might be some incidental similarities, they are only superficial; if you try to carry this analogy any reasonable distance it stops working. For example, when a person enlists in a branch of the US military, or goes to work for a company, the conditions of their employment are readily available in written form. A recruiter might suggest you talk to former service members to see if this is really what you want to do, while a cult "recruiter" would try to prevent such contact at all costs.
Additionally, employment and enlistment contracts either have an expiration date, or allow the employee to quit at any time (usually with the expectation of some notice of termination). Cult groups, however, want their members to "be involved" for the rest of their useful lives. My former pastor said (and probably still says) something like "there's no discharges from God's army!" You're pretty much in "Hotel California," the only difference being that they won't countenance any talk about checking out.
Justification for this behavior usually amounts to something like this: new members are not capable of understanding all the complexities of life in the group, so the group relieves them of the "burden" of having to accept everything at once. "Complex" or "advanced" doctrines or behaviors are then introduced as the member becomes accustomed to life in the group. Usually, the only "advanced" thing about these requirements is that they are so demanding that no free-thinking person would tolerate them without first undergoing sufficient indoctrination.
Below is a mock contract that should be applicable to almost any cult:
"By joining this group, I hereby agree to:
1. Devote every spare hour and dollar to the group, to be used at the leader's discretion.
I understand that I must subject myself to these rules, and any additional rules the leader imposes, no matter how strict, severe, or silly, for the rest of my life. Failure to do so may result in reprisal and/or eternal damnation."