Much probably the price/money is the first reason why people try to diy ,
and about the high price of professional audio devices ,
you can check a thread here around ,
that talk about however the distributors get high profit only moving pallets and boxes ,
contributing consistently to increasing the prices / cost of the units ,
if the price was lower , more units should be sold ,
and less people would be interested on the diy ,
as time is money , and diy require a good quantity of time (and "brain teasers" too…)
many prefer to use that time for recording , mixing , processing sound and make music
having more fun than work with electronics ,
earning money ,
to partially spend for buy units ,
except for who want to improve / customize or add more options to the units ,
or who also have available good quantity of free time , and electronics is the hobby ….
if the original units price were 30 / 60 % less
the number of sold units would be higher ,
only as simple example :
why buy Behringer if you can buy Golden Age Project audio processors ?
and :
have sense diy Golden Age Project audio processors ?
Also keep in mind that in the past (50,60,70,80,90 ages)
music productions had available big budgets to spend for rent recording studios and related "add-ons" ,
because records (vinyls) were sold (not downloaded)
and audio outboard prices were lower , (lower price more units sold ?)
then more moneys for all , (sexy "secretary"
included)
a more reach "market".