There are even much more adjectives ending in -e:
behände, etepetete, flügge, frigide, gelinde, gerade, greise, irre, kirre, klasse, knülle, krude, leise, lose, marode, meschugge, morbide, müde, mürbe, perfide, pleite, präzise, prüde, rege, rigide, rüde, schade, scheiße, schnöde, schnuppe, solide, vage, valide, weise
And of course there are some foreign adjectives, but they don't count in this case:
al dente, aubergine, benigne, liquide, live, beige, maligne, offline, offshore, online, papabile, up to date
But more interesting is this list:
alleine, bange, blöde, böse, derbe, fade, feige, milde, nahe, öde, rapide, sachte, spröde, stupide, träge, trübe, zähe
They all end in -e, but all of them have a second form without this ending -e, and (less obvious) they all have one syllable less:
allein, bang, blöd, bös, derb, fad, feig, mild, nah, öd, rapid, sacht, spröd, stupid, träg, trüb, zäh
Many German words end in a Reduktionssilbe. This is an unstressed syllable at the end of a word. The written form of such a syllable always contains the letter e as its vowel, and often there is no consonant after this e. In this case (a German word ending in an unstressed -e) this vowel is always pronounced as a mid central vowel [ə].
But in colloquial speech (which varies regionally) and in local dialects this vowel often is omitted:
Schule → Schul
Stunde → Stund
Leute → Leut
Auge → Aug
Aufgabe → Aufgab
You can find evidence of such omitted e's in many poems and lyrics, and it is usual to mark this omitted e with an apostrophe: »Schul’, Stund’, Leut’, ...«
Also many nouns used to end in -e in dative case:
old: dem Raume, dem Manne, dem Worte, ...
new: dem Raum, dem Mann, dem Wort, ...
When you compare German from 19th century with modern German, you will find, that many of those ending e's got lost, and this process is still going on, and it is transforming adjectives too. The adjectives with two forms are examples for this process, and the adjectives where only the form with -e exists, are just the ones that survived this process.