It's not necessarily about them hiding from us. It's about them loving us for who we are and respecting the free will of the collective consciousness.

As @Catherine mentioned in the comments to your question, earth has been in a quarantine zone. The quarantine is sort of a law that is respected by various alien beings. It prevents the beings who love and care for us as a one consciousness (yes there are those out there who don't respect our free will) to openly land in a public setting where their existence would be indisputable.

This quarantine is in effect until the date that is much talked about, December 21st 2012. After that date, any alien civilization that wishes to make open contact may do so as they please. As Bashar says though, it will then be up to us as a collective earth consciousness to get into the mode of being ready for this by raising our vibrational frequencies and allowing ourselves to accept the existence of alien beings.

At this time the collective consciousness of earth is not quite ready for this type of contact. We need to get to a slightly more positive side of the scale for this to happen. Once we become slightly more positive, and that starts to snowball, then you may very well see these beings start to test the waters in open contact in subtle ways.

They are waiting for us to be ready before they infringe on our free will. It's up to us to decide when we have open contact as a whole.

Here are a couple of videos from Bashar explaining the Quarantine.

Bashar On ET Contact process, timeline & 2012 end of quarantine on humankind

2012 - The End of the Earth UFO Quarantine

I think that this site sums it up pretty well. They go into a lot of theories, but most of them boil down to we are not ready. We are always fighting with ourselves and have many different Governments rather than one unified one. I guess the UN is kind of like that, but not really. Maybe one day when we stop being so violent and stop bombing each other they will think about it.

All and all I think that we need to grow up a lot before they do. If they exist that is.

I think it is similar to my question about how coming to Earth would be a bad decision. Humans are not always so friendly and welcoming. Some would try to capture one for a circus freak show, imagine the money you'd make "come see the real live space alien!" Then there are others that might try to shoot one and have it stuffed as a trophy. Others that would want to dissect it and find out what it is made of. This is if our government doesn't capture them first.

The we welcome you crowd is small. I forgot the we are being invaded shoot first ask questions later crowd. Earth can be pretty hostile, just look how we treat each other and we are the same species!