why do they canceled good show like early edition numbers moonlight, Kayl xy and Jericho then keep on show like big brother The Bachelor & The Bachelorette

They're NOT getting the ratings.

I like shows such as "Thunder Alley", "Titus", "Norm", and even "Kirk" (Kirk Cameron wasn't preachy on this show, mind you).

And "Gimme a Break" should've had one more year with Samantha Kanisky back, a proper finale with Nell, Grandpa, and Joey reminiscing life, and making it possible to have a spin-off show called "Samantha".

yep, that's what it's all about ratings especially in the 18-49 age group is the group the network goes after. Rumor has it that the network canceled Moonlighting due to Cybil Sheppard being difficult to work with and effected her relationship with Bruce Willis.

and even "Kirk" (Kirk Cameron wasn't preachy on this show, mind you).

For the record, I don't think Kirk Cameron's ever been preachy on any shows, except for ones where that's the point and nature of the show- like the Christian evangelism series he's done with Ray Comfort called "The Way of The Master".
But I get the distinction you were making.