Just back from using LBA as it is easier to use than Manchester from Scotland
via the A65, thus avoiding the M62
Just used aa routeplanner and google directions (having never done the route myself), both examples came out quicker and easier for Glasgow/Edinburgh-MAN than Glasgow/Edinburgh-LBA, with a time saving of over 20-25 mins for the former. Also both 'accounted for current reported traffic levels'
Also worth noting that from Scotland, the quickest route for both Glasgow and Edinburgh to MAN, the route goes nowhere near the M62. Thus, I have no idea which route you have been using, but seems you have been going well out of your way to need the M62 from Scotland.
At the end of the day, its not always down to ease why people don't use an airport, but rather the preference of airport. If people don't want to use airport A, then they wont.
However, in MAN's case, there are 22 million people who do 'find it easier' to use, and in LBA's case there are 2.9 million who are likewise.