Short answer: Egil's saga is not particularly more interested in legal matters than similar sagas.
I do not know what other sagas are being referenced in the question, but one should recognise that there are several types of sagas. The more important ones are sagas about Icelanders (Íslendingasögur), sagas about Kings (Konungasögur), and legendary sagas (fornaldarsögur). Egil's saga belongs to the first group. These typically focus on one or several conflicts on Iceland, or the travels of Icelanders, during the saga age, ca 870-1065 (which corresponds rather well to what is usually termed the "Viking age" in mainland Scandinavia).
Why were legal matters so important in general? First, it should be noted that Iceland was a free state. Iceland was settled by people a couple of steps down on the societal scale. Unlike e.g. the Orkneys, Iceland had no kings or even jarls until late in its history. It had "chieftains", and free farmers. It had a body for creating laws, and a judicial system, but there was no enforcement beyond what individuals were capable of. The law was a way for self-conscious chieftains and farmers to settle conflicts honourably.
Many saga heroes were sentenced to become outlaws, free for anyone to kill without repercussion. Other sagas tell of how the heroes will go to great lengths to avoid being forced into such positions by those harbouring ill will to the heroes (e.g. Njal's saga). Thus, since "conflict" is almost a genre marker, "dealing with legal matters" is also one.
For Egil's saga, legal matters are actually not very important to the plot; there is the inheritance that sometimes drives the conflict, but that is settled in Norway, and is not inherently important to drive things forward. Other legal matters are dealt with in self-contained episodes. It is in fact noted towards the end of the saga that Egil did not become embroiled in any major legal conflicts.
Robert Kellogg has written an introduction for the recent edition of all the sagas of Icelanders, simultaneously published in all Nordic languages. I have consulted the Swedish translation, i.e. in Islänningasagorna: Samtliga släktsagor och fyrtionio tåtar, first volume, for information about genre matters and Icelandic society. The first volume also contains Egil's saga, which I skimmed through to remind me of the legal episodes, since I could not remember that they featured at all.