कामैस्तैस्तैर्हृतज्ञानाः प्रपद्यन्तेऽन्यदेवताःतं तं नियममास्थाय प्रकृत्या नियताः स्वया
In plain words
Those whose jñāna is carried away by various desires resort to other deities, following this or that observance, constrained by their own nature.
Word for word
Those whose jñāna is carried away by this and that desire resort to other deities, having undertaken this or that observance, constrained by their own nature.
The commentators
Bhagavadgītābhāṣyam
आत्मैव सर्वो वासुदेव इत्येवमप्रतिपत्तौ कारणमुच्यते —
कामैः तैस्तैः पुत्रपशुस्वर्गादिविषयैः हृतज्ञानाः अपहृतविवेकविज्ञानाः प्रपद्यन्ते अन्यदेवताः प्राप्नुवन्ति वासुदेवात् आत्मनः अन्याः देवताः ; तं तं नियमं देवताराधने प्रसिद्धो यो यो नियमः तं तम् आस्थाय आश्रित्य प्रकृत्या स्वभावेन जन्मान्तरार्जितसंस्कारविशेषेण नियताः नियमिताः स्वया आत्मीयया ॥ २० ॥
In plain words
The Self alone is everything; everything is Vāsudeva. Why this is not recognized — the cause of that is now stated:
Driven by this desire or that — for a son, for cattle, for heaven, whatever it might be — people lose their knowledge, lose their power to discriminate, and go running after other deities, turning away from Vāsudeva, from their own very Self. Each one takes up whatever established observance fits the deity they've chosen, and holds to it. But underneath all of that, it's really their own nature doing the choosing — the specific imprint they carry forward from an earlier birth. That inherited nature is what constrains them, what shapes and limits where their devotion goes. It isn't imposed from outside. It's entirely their own.
Close to the Sanskrit
The cause is stated with regard to the non-apprehension thus — 'the Self alone is all, Vāsudeva' —
By this and that desire, whose objects are a son, cattle, heaven, and the like, those whose knowledge has been carried away, whose discriminating knowledge has been taken away, take refuge in, approach, other deities, apart from Vāsudeva, apart from the Self, other deities; having adopted, having resorted to, this or that rule, well-established in the worship of a deity, whichever rule, that very one, they are constrained, restricted, by their own, by their own inherent, nature, disposition, [namely] the particular latent impression acquired in a previous birth.