I afraid that I cannot offer a single definitive answer to 'why X didn't Y' type question of OP. Instead I'll make some corrections to OP's premise below.
First of all, there was no known unified large-scale kingdom in Scandinavia before the middle of the 10th century (until the rise of the Jelling dynasty in Denmark), possibly except for the kingdom of the Godfred family in its southernmost part (Southern Denmark) in the early 9th century. Three Nordic medieval kingdoms, that is to say, Denmark, Norway and Sweden have primarily been political products since the last decades of the first millennium. In other words, it was not so likely that the majority of the Norse raiders in the middle to late 9th century were under the direct influence of one of such rulers in the unified kingdom, though some Frankish rulers might have misunderstood so that they tried to negotiate the ruler of 'the Danes' to deal with the onslaughts of the raiders mostly in vain.
Apart from the apparent problem, navigation durability of the fleet of any non-Scandinavian power at that time from their homeland to Scandinavia (that I personally have much doubt), to annihilate or to conclude a treaty with one or two polities (petty kingdoms) in Scandinavia around 900 to stop raiding would not have eliminated the threat of Norse raiders' invasion since there were probably much more polities remained than the fleet could possibly handle.
And yes, there were indeed some attempt of non-Scandinavian European powers, especially some German rulers, to invade the southernmost part of Viking Age Denmark in the 10th century, as I illustrated in The Danes or Vikings from later Denmark would often raid the Frankish Empire and later what would become the Holy Roman Empire. How were they so successful and how did the Danes avoid being conquered by the big powers?. I suppose that main force of such German invasions comprised of cavalry and infantry, not the fleet, as long as attested in narrative sources and based on the location of the battlefield (Danevirke, the palisade built by Danish rulers).
On the other hand, I should also point out the fact that not all the Norse raiders didn't probably directly came to the British Isles from Scandinavia. Many Viking war bands were active around the British Isles as well as the English Channel in the middle of the 9th century, and now researchers suppose that they kept 'stayed' in this area for more than a few years, and sometimes took shelter in one of 'their' new political centers nearby, such as Dublin in Ireland or Rouen in Normandy, or further, York in Northern England, instead of Scandinavia. Then, targeting one of these 'diaspora' polities rather than distant petty kingdoms in Scandinavia would be much more realistic and successful tactic against the Norse raiders, and some local rulers actually did so (note that the Norse ruler was once expelled from Dublin in the early 10th century (from 902 to 917)).
References:
Were the Anglo Saxons really so unified for the most part of the Viking era?