The Purusha is the soul, and is the original creator of everything, but we think we are not responsible because we, of fragmented consciousness, perceive total separation from Prakriti and other Jivas.
Kapila Muni himself asserts the cause of bondage in his text "Samkhya Sutra":
Aph. 56.* Bondage arises from the error [of not discriminating between
Nature and soul].
Purport: The true cause of bondage, in other words, non-discrimination.
Aph. 50.* [We cannot admit that the soul is other than all-pervading;
because] by its being limited, since it would come under the same
conditions as jars, &c., there would be a contradiction to our tenet
[of its imperishableness].
Purport: Were the soul limited, it might be perishable.
Aph. 51.* The text regarding the motion [of the soul], moreover, is [applicable, only] because of the junction of an attendant; as in the
case of the Ether [or Space, which moves not, though we talk of the
space enclosed in a jar, as moving with the jar].
Purport: Soul moves not, any more than Space.
Aph. 52.* Nor, moreover, [does the bondage of the soul result from the
merit or demerit arising] from works; because these belong not
thereto.
Purport: The bondage of the soul is no result of any merit or demerit.
Aph. 53.* If the case were otherwise [than as I say], then it [the bondage of the soul might extend unduly, even to the emancipated].
Purport: Else, bondage might cling even to the emancipated.
Here Kapila is asserting that mere emancipation is not a switch which gets rid of any sort of bondage which prevents us from identifying the Purusha as the Jiva.
Aph. 54.* And this [opinion, that the bondage of the soul arises from any of causes alleged by the heretics,] is contrary to such texts
as the one that declares it [the soul] to be without qualities: and so
much for that point.
Purport: A single text of Scripture upsets, equally, all the heretical notions of the soul's relation to bondage.
But then, in that case, [some one may say], this conjunction of Nature and of the soul, whether it be essential, or adventitiously caused by Time or something else, must occasion the bondage even of the emancipated. Having pondered this doubt, he disposes of it as follows:
Aph. 55.* Moreover, the conjunction thereof does not, through non-discrimination, take place [in the case of the emancipated]; nor
is there a parity, [in this respect, between the emancipated and the
non-emancipated].
Purport: How the true cause of bondage affects not the emancipated.
This leads to Aphorism 56, which I've mentioned at the beginning.
Aph. 58.* It is merely verbal, and not a reality [this so-called bondage of the soul]; since it [the bondage] resides in the mind, [and
not in the soul].
Purport: The bondage of the soul is merely verbal, not real.
The existence of a bondage factor in these philosophies indicate that it is bondage indeed which prevents the Supersoul (Purusha) from identifying itself in a limiting condition (Jiva). However I have stated Kapila's exact verdict on how to remove this so-called unreal bondage.
Now lets skip over to Aphorism 71 and continue along to answer your second question.
Aph. 71.* The first product [of the Primal Agent, Nature], which is called 'the Great one,' is Mind.
By 'the Great one' is meant Mind.
Aph. 72.* 'Self-consciousness' is that which is subsequent [to Mind].
Purport: The relation of Self-consciousness to Mind.
Aph. 73.* To the others it belongs to be products thereof, [i.e., of Self-consciousness].
Purport: All products, save Mind, result from Self-consciousness.
Aph. 74.* Moreover, immediately, through that [i.e., the 'Great one' (Aph 71)] the first [cause, viz., Nature,] is the cause [of all products]; as is the case with the Atoms, [the causes, though not the immediate causes, of jars, &c.].
Purport: Nature, immediately the cause of Mind, is, immediately, the cause of all other products.
Aph. 75.* While both [Soul and Nature] are antecedent [to all products], since the one [viz., Soul,] is devoid [of this character of being a cause], it is applicable [only] to the other of the two, [viz., Nature].
Purport: Why Nature is the sole cause.
Aph. 76.* What is limited cannot be the substance of all [things].
Purport: Why the theory of a plastic Nature is preferable to that of Atoms.
Aph. 77.* And [the proposition that Nature is the cause of all is proved] from the text of Scripture, that the origin [of the world] is therefrom, [i.e., from Nature].
Purport: Scripture declares in favour of the theory.
So basically its Prakriti (nature), according to Samkhya, which is the sole cause of creation. Purusha is immovable without Prakriti.
Jivatmas are ultimately responsible for this manifestation, there's no why? for it. Its simply that the Jivatmas are themselves Purusha which had undergone the various procedures of Prakriti and have acquired this body-form. In reality the body is perishable, and without the limiting constraints of the body, all that remains is Purusha (ultimately).
However, if you want to know the "mechanism" of creation, its not covered in Samkhya Sutra.
