That's not the main reason why Titan did not do well in terms of sales.
Apart from the industrial dispute between Leyland and Park Royal during
the early production of Titan, as pointed out by ads190, another reason
of the poor sales of Titan was it is much too sophisticated, and its design
was too far ahead from its time. That was driven by the design input from
the engineers from London Transport, which Leyland identified as the main
customer. It turned the Titan to a design which suits London better than
anywhere else. In fact, the design of Titan bears a lot of similarity to the
last double decker designed specificly for London - the FRM1.
Leyland intended to develop the Titan as the replacement of their aging
Atlantean, Fleetline and VRT. However, the poor sale of Titan, coupled
by the emergence of competing products, esp. the Metrobus from MCW,
prompted Leyland to abandon the idea and develop the Olympian instead.
In all sense, the Olympian is a less sophisticated, and a relatively less
advanced design to the Titan.
Another major difference between the Titan and Olympian is the Titan
has independent front suspension, like the Routemaster and FRM1. It
proved so good that Volvo took up the design and incorporate it onto all
their low floor chassis design, including the B7TL, B9TL and B10TL.