As MC says, money was the usual reason.
None of the Stuarts sent out the army to collect taxes. Indeed, James I and Charles I only raised armies during military emergencies when the army had more important things to do. Most taxes voted by Parliament were collected by commissions of county gentlemen appointed by Parliament (they were named in the acts voting the taxes) and often included those who had sat as MPs. Some taxes were collected by professional tax collectors but they were always civilians. Although the king had permanent sources of revenues, everyone, including all the Stuart kings, accepted that Parliaments would need to be summoned from time to time to vote additional money, usually because of foreign wars.
The other major reason why Parliaments were needed was to pass legislation. Laws passed by Parliament carried greater authority and were easier to enforce.
Neither James I nor Charles I were Catholics and, like them, the overwhelming proportion of those who sat in their Parliaments were Protestants. Of the 547 men elected to the Long Parliament in 1640 and 1641 only three are known to have been Catholics. It took a whole series of purges between 1642 and 1648 to turn the Long Parliament into the Rump, but what made the difference was the purging of the moderate Protestants (and most of the extreme Protestants as well).
That any of the Parliaments before 1629 attempted to limit the powers of either James I and Charles I would be strongly disputed by many of the historians who are currently working on that period. Just because kings and Parliament fell out over particular issues does not mean that either side yet wanted to redefine the balance of power between them. It was not and is not at all clear that even after 1629 Charles I planned never to call a Parliament.