default vs default on

default is a noun but default on is not a noun.

Word	Noun	Adjective	Verb	Adverb
default	Yes	No	Yes	No
default on	No	No	Yes	No

As verbs, default and default on are synonyms defined as:

default (noun)	default on (noun)
loss due to not showing up
an option that is selected automatically unless an alternative is specified
loss resulting from failure of a debt to be paid
act of failing to meet a financial obligation

default (verb)	default on (verb)
fail to pay up	fail to pay up