"The key move was Congress’s amendment to INA §214(b), the provision that says every visa applicant is presumed to be an intending immigrant unless they prove otherwise. In 1990, Congress inserted an exception for H(i) and L nonimmigrants — i.e., it carved them out of that presumption. The current codification notes still show that this came from Pub. L. 101-649 §205(b)(1)" https://www.justice.gov/sites/default/files/eoir/legacy/2009...

Congress also added INA §214(h). In the 1990 Act, that new subsection said, in substance, that being the beneficiary of a preference petition under §204, or otherwise seeking permanent residence, does not count as evidence that the person intends to abandon a foreign residence for H(i)/L purposes. That is the clearest statutory confirmation of dual intent.

"Congress originally intended H-1B to permit temporary work status while also allowing pursuit of permanent residence. The House Judiciary Committee report reinforces that reading. It had a section titled “Dual Intent” and explained that this problem was especially burdensome for H and L beneficiaries, and that the bill treated the filing of an immigrant petition as not, by itself, proof that the person meant to abandon a foreign residence" (attached link is the legislative history) https://niwaplibrary.wcl.american.edu/wp-content/uploads/HR-...

"Congress added INA §214(h), providing that pursuit of permanent residence “shall not constitute evidence” of abandoning a foreign residence for H(i)/L nonimmigrants" https://www.justice.gov/sites/default/files/eoir/legacy/2009...

"H-1B is “coming temporarily,” while permanent residence is handled through the employment-based immigrant categories in §203(b) and adjustment under §245(a)" https://uscode.house.gov/view.xhtml?req=%28title%3A8+section...