Perhaps because the earth does not have legs? 'Rise up' is one of the definitions in the list you posted.
That's actually funny, how do you know the earth doesn't have legs? Have you looked at the under side of the earth?
I think there are other ways to make sense of the verse without inventing new meanings for Hebrew words or adding legs to the earth.
1c) (Polel) to raise up
1d) (Hithpael) to raise oneself, rise up
1e) (Hiphil)
1e1) to cause to arise, raise
1c) Polel is a rare stem formation. I don't think this is the form used in verse in question, maybe Stankann can confirm this.
1d) Hithpaelis the reflexive form, which doesn't seem to be the form used in the verse in question.
1e) Hiphil is the causative form, which neither seem to be the form used in the verse in question.
If you look at the biblical dictionary entry, you will see the verb is also used for rising up in violence or rising up in order to do something important, for example:
Psalm 17:7 (KJV)Shew thy marvellous lovingkindness, O thou that savest by thy right hand them which put their trust in thee from those that
rise up against them.
Psalm 139:21-22 (KJV)Do not I hate them, O Lord, that hate thee? and am not I grieved with those that
rise up against thee?
Translation "Raise up" is used in the sense of building something...
Isaiah 44:26Who confirms the word of His servant, And performs the counsel of His messengers; Who says to Jerusalem, ‘You shall be inhabited,’ To the cities of Judah, ‘You shall be built,’ And I will
raise up her waste places;
Isaiah 61:4 (KJV)And they shall build the old wastes, they shall
raise up the former desolations, and they shall repair the waste cities, the desolations of many generations.
...or bring on the scene
Genesis 38:8Then Judah said to Onan, "Sleep with your brother's wife and fulfill your duty to her as a brother-in-law to
raise up offspring for your brother."
Zechariah 11:16For I am going to
raise up a shepherd over the land who will not care for the lost, or seek the young, or heal the injured, or feed the healthy, but will eat the meat of the choice sheep, tearing off their hooves.
Recall, too, that word 'arise' in dictionaries like dictionary.com was in the context of rising when it came to natural phenomena:
https://www.dictionary.com/browse/arises
...
This is just the meaning of a word in English, but Isaiah was written in Hebrew, so it isn't relevant.
The fact that Strong-6965 is translated as Arise in many cases, doesn't mean that all English uses of Arise can be attributed to the Hebrew word. Do you speak other languages other than English? This is easier to understand if you are familiar with more than one language.
Instead of looking at English dictionaries maybe you could have a look at biblical Hebrew dictionary entry I posted earlier or at this link:
https://biblehub.com/hebrew/6965.htmI don't speak Hebrew and I'm not a bible expert, but I was able to find all this information just using google. What will happen when you debate someone who speaks Hebrew and knows the Bible? If you are serious about this I think you need to do more research and maybe learn some Hebrew and Greek.