We know because the guy who wrote it told us.
The guy who first wrote "eiland" spelled it as such. Then some idiot put an 's' on it as a stylistic choice to latinize a word that has no Latin root. Now if you spell it any way other than "island" you are wrong because that is the way to word is used and understood.
Or, to put it another way, if you want to insist language is set in stone let me translate for you:
Se mann þe ǣrest wrāt "eiland," swā hine stæfode. Þā sum dysig mann an 's' onlēde swā stīlcræft, tō Lǣden sprǣce þæt word þe næfþ nān Lǣden rōt. Nū gif þū hine stæfian on ǣnige wīsan būtan "island," þū bist wōh, forþām þæt is sēo wīs þe þæt word is gebrocen and understonden.
The maintenance and taxes on my home are far cheaper then rent in my area. I could not afford to rent the home I own.
People don't understand that a landlord is going to charge enough rent to cover all those costs and still make a profit. Otherwise they would just sell the home.