> (if I read right) there was no implementation of UAE before 2009

"Date: 2001-04-12 [...]
Fabio Alemagna began to port UAE to AROS so we can at least run Amiga binaries slowly.
[...]
Date: 2001-06-03 [...]
Fabio Alemagna [...] improved AROS' UAE port. UAE now works completely. This means that you can run your old software on AROS if a bit slow."
http://aros.sourceforge.net/news/archive/2001.php

More mentions of UAE:
http://aros.sourceforge.net/news/archive/2002.php
http://aros.sourceforge.net/news/archive/2003.php
http://aros.sourceforge.net/news/archive/2008.php

> so it was not really attractive to many, expecially compared to AmigaOS and MorphOS.

Yes, the reason for this has been the different level of integration of m68k emulation. Even o1i's slightly better integrated Janus-UAE with coherency mode starting in 2009 couldn't quite change that.