Training is short-lived and event-based
When training occurs on one or two days every once in a while, it creates short-lived excitement and short-lived skill uptake and on-the-job application.
Training is in a bubble
Classroom training tends to be removed from the day to day work experience of the participants, both in terms of time and real world application.
Training is now or never
When an employee misses a training class due to other obligations or due to starting employment after the class, he/she is left behind until there is another opportunity to take the class and by that point the class may be “history” to the rest of the group.
For more issues with classroom-based training and alternative solutions you might consider, have a look at my full post at Intuit's Fast Track blog.