Why do you buy new brushes

[IRISHCOAST]

Everyone to their own when it comes to brushes, but for me personally I use nothing but the Omega 49 boar with a 27mm knot and 57mm loft, The handles are a lot to be desired but had them replaced by Bernd at Shavemac and very reasonable too. (7 in rotation)
The Omega 49 has a lovely face feel once broken in (about 20 lathers to break in) an IMO will match ANY badger brush whipping up lather, soaps, creams or anything else you throw at it, bowl or face lathering it will do the business and do it well, a salt spoon of cream is enough to make lather for at least 3 passes.
At around £9 you can't go wrong

 

[Irfan]

When I first got into shaving I wanted to buy the best brush that money could buy. With very little knowledge I got a silver tip badger, £70 Muhle. It still gets used lots.
My second brush was for traveling, a synthetic.
I only bought two more, one boar and one mixed boar. Mainly because of MWF, they do a good job.
Although I'm an obsessive shaver, I'm not planning on getting many (if any) more.
So, in answer to your question, as pretty as I think they look on my bathroom cabinet, I've convinced myself that all of my decisions are based on logic and practicality. This makes less sense with my last two purchases because I clearly only needed one more brush.
And, as I stay active on the forum I'm certain that I'll convince myself that I only need one more, then maybe another one...

 

[Batch300]

Oniomania

Also called Compulsive Buying Disorder. CBD is characterized by an obsession with shopping and buying behavior that causes adverse consequences. According to Kellett and Bolton, compulsive buying "is experienced as an irresistible–uncontrollable urge, resulting in excessive, expensive and time-consuming retail activity [that is] typically prompted by negative affectivity" and results in "gross social, personal and/or financial "credit card" difficulties". Most people with CBD meet the criteria for a personality disorder. Compulsive shopping may be considered an impulse control disorder, an obsessive-compulsive disorder, a bipolar disorder,[3] or even a clinical addiction, depending on the clinical source.

FYI - oniomania (from Greek ὤνιος ṓnios "for sale" and μανία manía "insanity"