Apparently employees were told to invest in the company or they would be denied payment/bonuses. Feel sorry for everyone involved in this dumpster fire.
Even towards the end the CEO was taking out personal loans secured on his Enron shares... in order to buy more Enron shares. This was a big contributor to the snowball effect when the share price started falling. I think the top people at Enron honestly believed in the stock and were probably mostly pushing it for employees on this basis. That was pure hubris, thinking they were smarter than everyone else. They should have known better and some were rightfully prosecuted for their part, but it's a bit more complicated than saying the employees were "tricked".
Of course, there was a corporate pension as well that failed and was was also largely in Enron stock. So now those liabilities are owned by the PBGC.