Bamboo is not really illegal in the US, although there are some regulations on bamboo in the US, mainly due to the invasive nature of bamboo.
The US restrictions on bamboo, especially the running bamboo varieties are a result of it's invasive nature and potential for damage.
Bamboos aggressive underground root system, or rhizomes, can spread up to 15 feet per year and push through concrete cracks, utility lines brickwork etc, and the rapid spread also allows the bamboo to out-compete and displace plant species that are native to the area and harm local ecosystems.
The negatives of bamboo are that bamboo is aggressive, invasive and spreads via underground roots called rhizomes, which can damage property as well as out-compete native plants.
Other negatives of bamboo are that there are durability issues like bamboos susceptibility to rot, and susceptibility for insects and mold if untreated, which requires significant chemical processing for construction, and also maintenance challenges.
These negatives of bamboo, make the bamboo less eco friendly than bamboo appears to be due to intensive processing and potential for use of chemicals.
Running bamboo is highly invasive and spreads rapidly, which cracks concrete, damages foundations and overtakes ecosystems and yards.
Bamboo has an extensive root system, called rhizomes that is hard to eradicate, sometimes requiring herbicides.
And bamboo is a threat to biodiversity, it can shade out and even displace native plants and harms local habitats.
Untreated bamboo rots and molds and attracts insects like borers and termites.
And to be durable, the bamboo needs preservatives, often involving chemicals like formaldehyde/arsenic, adding costs as well as potential environmental concerns.
Bamboo can also crack, splinter or split over time and variability between species makes standardization difficult for large process and bamboo is less fire resistant than wood.
Turning raw bamboo into usable products also requires energy and often harsh chemicals, which offsets some of the eco benefits of bamboo and sourcing and transporting bamboo can also negate it's local benefits.