I may be totally wrong, but this is what i think: when a tank is knocked out, it is clear, that it can't be used any more, damage is just too critical. Think about it: would you stay in a tank, that has been set on fire ? And then of course a penetration may have killed some of the crew, a driver for example, so it just can't continue. The crew will bail out.
When a tank is abandonded, there may be many reasons: if it is immobilized or a gun is damaged and crew thinks, that is is much more dangerous to stay in it than to run away, they will abandon it. And of course, if you hammer it enough with guns, crew may panick and abandon it, because they fear that one of those shots will penetrate the tank.
Welcome to the forum, by the way, and sorry of you find this difficult to read. I'm not a native english speaker, nor am i very good at it.