So why do Sith even seek and acquire apprentices if the Rule Of Two necessitates that the apprentice must crave his master's power and eventually kill him. Do the Sith know this will happen and just not care or are they suicidal or what?
Because they can't live forever? The point is that when their time eventually comes they will be replaced by someone stronger. Someone who can continue the Sith and eventually take over the galaxy and wipe out the Jedi. Doing anything else would either doom the Sith to extinction (taking no apprentice at all), or weaken them (an apprentice not strong enough to kill their master).
The Rule of Two (which is more of a guideline than a rule) was set in place to ensure only the strongest leader survived if a single apprentice defeats their master the master was weak and unfit to lead (the Sith have a somewhat twisted Darwinian world view)
The question however was why take an apprentice at all and the answer is to grow stronger, at a certain point the only way to learn is to teach someone what you know.