Gravity is relevant to the growth of the egg.
As we know, the eggs need to be on a flat surface, preferably the ground. Under low gravity conditions, that limit is reduced and surfaces on walls and floors become viable. Even upside down. Of course, limitations still exist but the egg would be able to grow to full size before gravity starts to affect it. The contents of the egg would increase in mass as it grows and eventually, even reduced gravity would be sufficient to influence the egg to releasing its contents onto the floor.
The fact that the egg is forced to disgorge its contents under these conditions means it does so without the need for a host to approach.
-Windebieste.
EDiT. As for the spores being dropped, there's ample opportunity for the Queen to drop them from her, um, vulva(?). How many long shots of the Queen are there compared to her duration on screen? How often do we see the full floor decking? There's so many close up shots of Ripley operating the loader and the Queen's head, just pick a moment or two. ...or three.
Of course the characters wouldn't notice... Ripley was too engaged in avoiding getting her face pulled off. Bishop was lying on the floor in pieces and Newt was hiding under the grates.
There was no one else to stand back and say "Ooh... what did the Queen just drop? I guess I'd better go clean up that mess when this fight is finished. Where's my popcorn?"