Sorry for the long-winded post... TL/DR: some band members and soloists don't like wearing the clothes but still want to play the music.

Ladies and gents of XMarks, believe it or not there are those in the piping community - soloists and band members - who love the music (playing and listening) but really dislike the hassle of the wardrobe requirements. Those folks would just as soon wear their shorts/jeans and polo/tee shirts like they do at home or at band rehearsal when practicing than have to put on this awkward, uncomfortable - hot, itchy, ill-fitted, etc. - "costume" (fancy dress for those on the east side of the big water) when playing their instrument. (The attitude affects both pipers and drummers.)

Even though the pipe band associations (the EUSPBA is one) no longer judge a musical competitor on 'dress & deportment', most of the games venues that sponsor a piping/drumming/band competition have a 'Highland dress/garb required' clause for entrants.

Part of the "I don't wanna wear it" attitude may be due to the cost and/or the fit. Bands typically issue a kilt that is 'close' (maybe) to the right fit rather than order a new kilt made to measure for a new band member that may not stay more than a few months. Items beyond the kilt are usually personal-purchase items anyway, though the band may offer something 'at cost' if they order uniform items in bulk (mainly kilt hose).

Those not affiliated with a band have to spend as much or more on their wardrobe items than they do on their instruments, at least in their first year or so of competition. A decent set of pipes will run about US$800 or so, fully set up. (I'm sure less expensive sets can be found, depending on region and materials - I'm ball-parking an average cost.) Kilt, hose, jacket/waistcoat (or both), and headgear run at least that much, unless one is fortunate enough to find things on a bidding site, thrift shops, etc. A lot of new-ish competitors may not have the time (or patience) to wait for items to come up - "I'm entered in my first contest in a month and still have to get my 'outfit' together! Time to rush-order from 'Scottish clothing website du jour'!"

Another thing a lot of those outside the piping community don't realize is that the massed bands spectacle that many spectators/listeners enjoy is mind-numbingly boring to many of the performers due to the relative simplicity of the tunes - the selection is often limited to the repertoire of the lowest-grade band so every band can play - and/or the clash of different settings (different embellishments, etc. - not everyone plays/learns the "standard settings" found in the tune books e.g. Scots Guards Standard Settings of Pipe Music Vol I). Massed bands also tend to be stuck out on a hot, open field for long periods of time listening to endless speeches by organizers, various guests/dignitaries, lists of the days winners in the various activities, etc., etc. This affects the tuning/playability of the instruments (and that of the players!).

Bands also tune to slightly different pitches which blend together at a distance but are very obvious 'in the ranks'. This really annoys the band members that actually listen to the players around them for their musical cues. (Are my pipes flat or sharp to the piper next to me? Should I blow/squeeze harder to go sharp or ease off a bit to go flat? Oops, too sharp for the one to the left of me, but the guy to my right is even sharper than ME!)

Another thing that annoys bands about playing in massed bands is that a lot of bands that come to a Highland Games venue for a band competition tend to be bands that don't practice a lot of marching, especially the 'close order drill' kind of marching that sees a block turning in a left/right wheel, counter-marching, etc. that's why you'll see a lot of 'crab walking' or sideways movement of the back end of a block rather than lines that pivot on one end like well-drilled parade/marching units do.

Just some observations from a piper & former Pipe Sergeant of a competition band. My own opinions and not intended to be all-encompassing hard-and-fast "rules" or statements of 'facts'.