Gaussian blur only blurs the interior of primitive?

Question

I cannot work out why my blur shader based on this example affects only what's inside the illuminated sphere. Below is the loop I'm using to blur an HDR framebuffer 5 times horizontally and vertically

for(let i = 0; i!=5; i++){
    gl.bindFramebuffer(gl.FRAMEBUFFER,BlurFBOH);
    gl.viewport(0,0,canvas.width,canvas.height);
    gl.clearColor(0,0,0,1);
    gl.clear(gl.COLOR_BUFFER_BIT|gl.DEPTH_BUFFER_BIT);
    
    setUniformInt(BlurShader,"HV",1);

    if (iteration == 0) {
        gl.bindTexture(gl.TEXTURE_2D, HDRTex);  
    }
    else {
        gl.bindTexture(gl.TEXTURE_2D,blurredTexV);
    }
    renderQuad(BlurShader,quadVAO,ID,ID,ID);
    gl.bindFramebuffer(gl.FRAMEBUFFER,null);
    
    gl.bindFramebuffer(gl.FRAMEBUFFER,BlurFBOV);
    gl.viewport(0,0,canvas.width,canvas.height);
    gl.clearColor(0,0,0,1);
    gl.clear(gl.COLOR_BUFFER_BIT|gl.DEPTH_BUFFER_BIT);
    
    setUniformInt(BlurShader,"HV",0);
    gl.bindTexture(gl.TEXTURE_2D,blurredTexH);
    renderQuad(BlurShader,quadVAO,ID,ID,ID);
    gl.bindFramebuffer(gl.FRAMEBUFFER,null);
    iteration++;
}