Samsara and our consequent rebirth there is created by natural laws...the main one being the law of karma and change.

But why not just have Nhibbana and nothing else?

If you speak of natural laws, how/why would Devas engage sexually?

Sex is an evolutionary/darwinian way of reproducing thus continuing the species.

Sexual enjoyment ensures engagement and thus reproduction.

If Devas in the heaven realms do not reproduce, what natural law/evolution would produce sexuality?

Also, wouldn't the pleasure of sexuality pale into insignificance in comparison to heavenly experience?

But more importantly what of "the previous cuti-citta and next patisandhi-citta not being the same.

Does awakening stop the "causal continuum", or stream of consciousness, or does it stop punabbhava ("further" or "renewed" becoming) and upapattibhava ("resultant" becoming or existence)?

Awakening stops the second two, in four successive stages and as the fourth stage is realised, the causal continuum also ceases. All that survives is magga-citta (path-citta), a supramundate citta whose object is nibbana.

As for the other questions, I would say they tend not to edification, ie, as far as I can recall, they're not answered in the Tipitaka so any answers would be speculative.

I don't think a comparison with photocopies or clones quite applies because aggregates arise according to vipaka, that is the result of kamma. Since vipaka experienced in this set of aggregates would no longer apply, the next set would be linked to different vipaka. Hence the form taken could be very, very different. Obviously there is no way to know for sure.

I forgot to add.

Finally, if it's the aim to end dukkha and be free from the cycle of re birth, why have it and samsara in the first place?

Nibbana is the goal of those who follow the Buddhas path and thus know about it....but there are many who do not know. Only rarely do we get the chance to know this...and then to act upon this knowledge is up to us.

It is like asking the christians why if the goal is heaven did their god decide to have beings born in order to play a game of chance whether they would reach the goal or not... why not just put them all there?

No ultimate being created the universe and life...it is all a result of natural causes and effects....helped along by laws of karma.